Step 1: Create private endpoint for your web app
1. In the left-hand menu, select All Resources > caption12345678 - the name of your web app.
2. In the web app overview, select Settings > Networking.
3. In Networking, select Private endpoints.
4. Select + Add in the Private Endpoint connections page.
5. Enter or select the following information in the Add Private Endpoint page:
Name: Enter caption12345678.
Subscription Select your Azure subscription.
Virtual network Select VNet1.
Subnet: -
Integrate with private DNS zone: Select Yes.
6. Select OK.
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Reference:
https://docs.microsoft.com/en-us/azure/private-link/tutorial-private-endpoint-webapp-portal