Even though you already have an admin account, this may still happen. You just need to create a temporary new admin account to bypass the issue. Follow the steps below: Start your Mac normally to the desktop. Go to Apple logo > System Preferences > Users & Groups. Unlock the yellow lock at the right bottom with your admin password. Click + to add a new admin account and click Create User to confirm. Shut down the Mac, boot the Mac into Recovery Mode and then reduce security with the newly created admin account. Delete the new admin account after your Mac restarts.