that sounds like you didn’t install some debian package.
in that case, you’ll have to find out where the install copied all those files to. it’ll be the usual locations of header files, library files (.a or something?), and shared objects. try the same make install again and hopefully it prints a lot of paths, that you can delete.
if you never did a make install (or apt install something of a premade package), you didn’t actually install the library, just build it. in that case, all the headers, libs, and shared objects just hang out in the build directory of your copy of OpenCV, and maybe in an install directory, which is a kind of “redistributable” for development