This is a manual process if the directories are already cased properly locally. The problem is that by default git ignores case changes for filenames and directory names. Here is an answer explaining how to change that (though not recommended, read comments), and here’s a potential fix if the files/folders are not cased properly locally.
Check out a Pull Request on the original repo when I have a fork on my local machine
The GitHub PR page includes instructions for checking out a PR on the command line, but if you are running a fork locally, you need to work with the upstream branch instead of the origin branch.