I don’t know how long ago you last used Lexicon but it may have been a beta version that was quite different.
There are Lexicon backups you can restore from in your Documents/Lexicon/Backups folder and for Rekordbox 6 there are backups too. You can find them here Lexicon with Rekordbox 6 write support and then look in the Lexicon folder.
@StuR is asking the right questions, we need to know more before we can give you useful answers as to what happened here.
If you’re restoring from a RB backup, you can import again from RB and make sure to leave the Merge option off. That will delete your Lexicon library and mirror what you have in RB.