C++ .cpp and .h files can't locate includes

Hello, I’m having an issue in the .cpp and .h files for a new project I’m working on. I’m trying to include a plugin I made in a previous project, but for some reason, the includes in both the .cpp and .h files can’t be located. I’m getting E1696 errors saying “cannot open source file ‘file name’”. I’ve seen other similar questions on this forum, and the solutions for them are to open the editor and refresh the code. However, I can’t open the editor. It asks me to rebuild the modules because they’re for a different engine version (I made them for 5.2, and this project is in 5.5), but when I do, it says “‘project name’ could not be compiled. Try rebuilding from source manually.” What can I do to resolve this issue?