How to Upgrade Net Core 3.0 project to Net Core 3.1 in Visual Studio 2019 16.4 Preview 5

# Issue Title

Be as descriptive as you can with your title.

# General

Provide details on the problem you are experiencing including the .NET Core version, operating system version and anything else that is relevant.

Please provide a code sample for your issue if it is relevant, either inline, link to a gist (or similar) or add it as a zipped attachment.

For some issues, you will get a quicker and better response if you file it at a more specific [.NET repo](https://github.com/dotnet/core/blob/master/Documentation/core-repos.md). For example, if the problem is with ASP.NET Core, you are encouraged to use the [aspnet/home repo](https://github.com/aspnet/home/issues).