fix script

Author: gitName

includes/api-management-virtual-network-address-prefix.md

@@ -15,10 +15,14 @@ If you configure the subnet using the Azure portal, the subnet sets an `addressP
 To create or update a subnet with `addressPrefix`, use a tool such as Azure PowerShell, an Azure Resource Manager template, or the [REST API](/rest/api/virtualnetwork/subnets/create-or-update). For example, update a subnet using the [Set-AzVirtualNetworkSubnetConfig](/powershell/module/az.network/set-azvirtualnetworksubnetconfig) Azure PowerShell cmdlet:
 
 ```powershell
-$virtualNetwork = "MyVirtualNetwork"
+$resourceGroupName = "MyResourceGroup"
+$virtualNetworkName = "MyVirtualNetwork"
 $subnetName = "ApimSubnet"
 $addressPrefix = "10.0.3.0/24"
 
+
+$virtualNetwork = Get-AzVirtualNetwork -Name $virtualNetworkName -ResourceGroupName $resourceGroupName
+
 Set-AzVirtualNetworkSubnetConfig -Name $subnetName -VirtualNetwork $virtualNetwork -AddressPrefix $addressPrefix
 
 $virtualNetwork | Set-AzVirtualNetwork