This is a guess gathoni and there is no way I can find the answer for you. Normally, functions are all lumped together in a single file someplace. They are loaded to a page with the require ("function_file_name") at the top of the php. This maybe commented out or was erased. If this don't work for you you can open each file you have and search for
I know that's way too little, but it's the best I have.