Day 0 support for .NET 7.0 on App Service means that developers are immediately unblocked to try, test, and deploy .NET apps targeting the version of .NET accelerating time-to-market on the platform they know and use today. It is expected to be available in Q2 FY23.
Please visit this QuickStart: Deploy an ASP.NET web app to try out .NET 7.0 on App Service.