How do I uninstall a program that cannot be uninstalled normally?

I wanted to uninstall a program that no longer works properly. The problem with the program existed before and the problem was solved by uninstalling and reinstalling it. The first time, this program could be uninstalled as normal. But now the program is no longer in the list of programs that can be uninstalled. My only option is to remove the program manually, but how do I do that? How do I remove the program manually so that I can reinstall it cleanly later?