How to extend WixUI_InstallDir

[romanitodua]

Given the following code

	 xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
	<Package Id="TODO_Manufacturer.testingwix"
			 Name="testingwix"
			 Manufacturer="TODO Manufacturer"
			 Version="1.0.0.0">
		<MajorUpgrade DowngradeErrorMessage="!(loc.DowngradeError)" />
		<Feature Id="Main">
			<ComponentGroupRef Id="ExampleComponents" />
		</Feature>

		<ui:WixUI
			Id="WixUI_InstallDir"
			InstallDirectory="INSTALLFOLDER"
        />
		<WixVariable
			Id="WixUILicenseRtf"
			Value="C:\LICENSE.rtf"
		/>

	</Package>

	<Fragment>
		<StandardDirectory Id="ProgramFiles6432Folder">
			<Directory Id="INSTALLFOLDER" Name="!(bind.Property.Manufacturer) !(bind.Property.ProductName)">
			</Directory>
		</StandardDirectory>
	</Fragment>

	<Fragment>
		<ComponentGroup Id="ExampleComponents" Directory="INSTALLFOLDER">
			<Component Guid="*">
				<File Source="App.exe" />
			</Component>
		</ComponentGroup>
	</Fragment>
</Wix>

How can i add a custom dialog into this UI that will ask the user to locate a file called example.txt(if its not present in the working dir) and then copy that file into the installation directory
I have tried just using source code of installDir UI but thats behaving same as just using the namespace I tried following this to try to add a dialogue , but instructions are not very clear to me they are surface level

[romanitodua]

<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
	<Package Name="MsiPackage" Language="1033" Version="1.0.0.0" Manufacturer="Example Corporation" UpgradeCode="047730a5-30fe-4a62-a520-da9381b8226a" InstallerVersion="200">
		<MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />

		<Feature Id="ProductFeature" Title="MsiPackage">
			<ComponentGroupRef Id="ProductComponents" />
		</Feature>

		<ComponentGroup Id="ProductComponents" Directory="INSTALLFOLDER">
			<Component>
				<File Source="C:\Users\rtodua\zig-com\App.exe" />
			</Component>
		</ComponentGroup>

		<ui:WixUI Id="InstallDir_License" InstallDirectory="INSTALLFOLDER" />
		<Property Id="CONFIG_PATH">
			<DirectorySearch Id="CONFIG" Path="[SourceDir]" Depth="0">
				<FileSearch Id="TOOL_EXE_SEARCH" Name="testconfig.config" />
			</DirectorySearch>				
		</Property>
		
	</Package>

	<Fragment>
		<StandardDirectory Id="ProgramFilesFolder">
			<Directory Id="INSTALLFOLDER" Name="MsiPackage" />
		</StandardDirectory>
	</Fragment>

	<?foreach WIXUIARCH in X86;X64;A64 ?>
	<Fragment>
		<UI Id="InstallDir_License_$(WIXUIARCH)">
			<Publish Dialog="BrowseDlg" Control="OK" Event="DoAction" Value="WixUIValidatePath_$(WIXUIARCH)" Order="3" />
			<Publish Dialog="InstallDirDlg" Control="Next" Event="DoAction" Value="WixUIValidatePath_$(WIXUIARCH)" Order="2" />
		</UI>

		<UIRef Id="InstallDir_License" />
	</Fragment>
	<?endforeach?>

	<Fragment>
		<UI Id="file InstallDir_License">
			<TextStyle Id="WixUI_Font_Normal" FaceName="Tahoma" Size="8" />
			<TextStyle Id="WixUI_Font_Bigger" FaceName="Tahoma" Size="12" />
			<TextStyle Id="WixUI_Font_Title" FaceName="Tahoma" Size="9" Bold="yes" />

			<Property Id="DefaultUIFont" Value="WixUI_Font_Normal" />

			<DialogRef Id="BrowseDlg" />
			<DialogRef Id="DiskCostDlg" />
			<DialogRef Id="ErrorDlg" />
			<DialogRef Id="FatalError" />
			<DialogRef Id="FilesInUse" />
			<DialogRef Id="MsiRMFilesInUse" />
			<DialogRef Id="PrepareDlg" />
			<DialogRef Id="ProgressDlg" />
			<DialogRef Id="ResumeDlg" />
			<DialogRef Id="UserExit" />

			<Publish Dialog="ExitDialog" Control="Finish" Event="EndDialog" Value="Return" Order="999" />

			<Publish Dialog="WelcomeDlg" Control="Next" Event="NewDialog" Value="LicenseAgreementDlg" Condition="NOT Installed" />
			<Publish Dialog="WelcomeDlg" Control="Next" Event="NewDialog" Value="VerifyReadyDlg" Condition="Installed AND PATCH" />

			<Publish Dialog="LicenseAgreementDlg" Control="Back" Event="NewDialog" Value="WelcomeDlg" />
			<Publish Dialog="LicenseAgreementDlg" Control="Next" Event="NewDialog" Value="InstallDirDlg" Condition="LicenseAccepted = &quot;1&quot;" />

			<Publish Dialog="InstallDirDlg" Control="Back" Event="NewDialog" Value="LicenseAgreementDlg" />

			<Publish Dialog="InstallDirDlg" Control="Back" Event="NewDialog" Value="WelcomeDlg" />
			<Publish Dialog="InstallDirDlg" Control="Next" Event="SetTargetPath" Value="[WIXUI_INSTALLDIR]" Order="3" />
			<Publish Dialog="InstallDirDlg" Control="Next" Event="NewDialog" Value="VerifyReadyDlg" Order="4" />
			<Publish Dialog="InstallDirDlg" Control="ChangeFolder" Property="_BrowseProperty" Value="[WIXUI_INSTALLDIR]" Order="1" />
			<Publish Dialog="InstallDirDlg" Control="ChangeFolder" Event="SpawnDialog" Value="BrowseDlg" Order="2" />

			<Publish Dialog="BrowseDlg" Control="OK" Event="SetTargetPath" Value="[_BrowseProperty]" Order="3" />
			<Publish Dialog="BrowseDlg" Control="OK" Event="EndDialog" Value="Return" Order="4" />

			<Publish Dialog="VerifyReadyDlg" Control="Back" Event="NewDialog" Value="InstallDirDlg" Order="1" Condition="NOT Installed" />
			<Publish Dialog="VerifyReadyDlg" Control="Back" Event="NewDialog" Value="MaintenanceTypeDlg" Order="2" Condition="Installed AND NOT PATCH" />
			<Publish Dialog="VerifyReadyDlg" Control="Back" Event="NewDialog" Value="WelcomeDlg" Order="2" Condition="Installed AND PATCH" />

			<Publish Dialog="MaintenanceWelcomeDlg" Control="Next" Event="NewDialog" Value="MaintenanceTypeDlg" />

			<Publish Dialog="MaintenanceTypeDlg" Control="RepairButton" Event="NewDialog" Value="VerifyReadyDlg" />
			<Publish Dialog="MaintenanceTypeDlg" Control="RemoveButton" Event="NewDialog" Value="VerifyReadyDlg" />
			<Publish Dialog="MaintenanceTypeDlg" Control="Back" Event="NewDialog" Value="MaintenanceWelcomeDlg" />

			<Property Id="ARPNOMODIFY" Value="1" />
		</UI>

		<UIRef Id="WixUI_Common" />
	</Fragment>
	
</Wix>

This is what I've got so far , I'd like to display a dialog based on if the file was present and then copy it to installdir