Update Update-AzVpnGateway.md (#17787)

* Update Update-AzVpnGateway.md

I worked with Deepak Narula to create commands to remove custom BGP IP from virtual wan vpn gateway and set them back to default.

* Update src/Network/Network/help/Update-AzVpnGateway.md

Co-authored-by: Yeming Liu <[email protected]>

Co-authored-by: Yeming Liu <[email protected]>

Author: brwurz

src/Network/Network/help/Update-AzVpnGateway.md

@@ -106,6 +106,20 @@ A VPN gateway will be created thereafter in the Virtual Hub with 2 scale units.
 
 After the gateway has been created, it uses Set-AzVpnGateway to update BgpPeeringAddress.
 
+### Example 3
+
+```powershell
+$gw = Get-AzVpnGateway -ResourceGroupName "testRg" -Name "testgw"
+$gw.BgpSettings.BgpPeeringAddresses
+$gw.BgpSettings.BgpPeeringAddresses[0].CustomBgpIpAddresses=$null
+$gw.BgpSettings.BgpPeeringAddresses[1].CustomBgpIpAddresses=$null
+$gw.BgpSettings.BgpPeeringAddresses
+Update-AzVpnGateway -InputObject $gw
+```
+The above will update the Virtual WAN VPN Gateway to use the default BgpPeeringAddress.
+
+It uses Update-AzVpnGateway to update BgpPeeringAddress
+
 ## PARAMETERS
 
 ### -AsJob
@@ -340,4 +354,4 @@ This cmdlet supports the common parameters: -Debug, -ErrorAction, -ErrorVariable
 
 [New-AzVpnGateway](./New-AzVpnGateway.md)
 
-[Remove-AzVpnGateway](./Remove-AzVpnGateway.md)
+[Remove-AzVpnGateway](./Remove-AzVpnGateway.md)