Going back to the last version of logic

No need to "erase" the current version of Logic. Different Logic versions can be placed next to each other in the application folder as long as they are re-named differently, the current version should not be re-named. Alternatively – if you won't use the current version no longer, you could zip this version, keep the zipped version somewhere on your hard drive, than delete the uncompressed Application.

Now, just retrieve an old Logic version from your backups, rename and place it into the application folder.

For this reason, Apple strongly recommends backing up Logic before updating.

Back up Logic Pro for Mac - Apple Support