I have git installed, and from Tools->Git->Diff, I can select Apply Chunk or Revert Chunk

On Linux it works, but on Windows it gives me
Unable to launch 'patch': Process failed to start: No such file or directory
Where do I need to install this patch.exe, and where do I get it from?
There actually was patch.exe that came with Git, but it was located at “C:\Program Files\git\bin”, and that wasn’t added to PATH. I think that was because I didn’t select the right option in the Git install wizard.
Qt Creator allows you to specify where the patch command is in its settings (the “Patch command” in the screenshot below).