How to restore an environmental variable on Windows 10

Ok, I did a really, really stupid thing the other night while trying to install JDK 1.6 (older version, I know, but it's for an online class I'm taking and for some reason that's the version the teacher is using).

I went to environmental variables to create a path for my Java and inadvertently deleted the original environmental path, so, of course, I caot even launch JDK.

How can I reinstall the original path on Windows 10? I tried regedit but am a little clueless where to go from here.

Thanks a million!