Unload required project. After that you can edit “.csproj” file. Delete everything and write the next code:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>

    <TargetFramework>netstandard2.0</TargetFramework>

  </PropertyGroup>

</Project>

Delete “AssemblyInfo.cs” file in the “Properties” (.NET standard does not need it).

Install/Reinstall NuGet package which are compatible with .NET standard.

At the end you can delete “packages.config” (it should be the last because you are using it as a reference to what packages your project depends on).

Also you do not need “app.config” file, but you can use it in .NET standard and .NET Core, but this not a correct way to proceed.

Remarks: sometimes you should reinstall in other not converted to .NET standard projects some System libraries from the NuGet repositories, for example : ”System.Configuration.ConfigurationManager”,” System.Data.SqlClient”.