Sorry to hear about the issues you are facing. We are open to the feedback.
Are you using community edition? If yes - I believe all the users have admin privileges. So you could just create yet another user and it would be an admin, unless now you can’t even login with any user (you forgot all the users you created).
If it is enterprise edition you could use LDAP to not deal with users internal and known only to Dremio.
Regarding reinstall not helping. All the essential data is kept in Dremio internal key/value store that probably stored independently from your install directory (most likely in /var/lib/dremio) and as it is not getting deleted you still get everything as it was before you reinstalled software.