You could create a new project using the React template, and then use that as a reference to help upgrade your existing project. ASP.NET MVC is always so particular about it's configuration and where files should be put, so I've always found it helpful to work with an example. something something monkey see monkey do.
See here how for to create said template: https://learn.microsoft.com/en-us/aspnet/core/client-side/spa/react?view=aspnetcore-5.0&tabs=visual-studio
And if CLI isn't your favorite, if have a recent version of Visual Studio IDE or Rider IDE you can create the a new project with the react.js template/option selected.