1st step to try: re-flash your mSD card with latest UmbrelOS 0.4.8
If is still locked, go to step 2:
ssh -t umbrel@umbrel.local
The prompted password is your dashboard password.
Then execute:
cd ~/umbrel && docker-compose exec lnd /bin/bash
Then:
lncli unlock
When prompted, enter the password moneyprintergobrrr
Done. Now open Umbrel dashboard page and login.