Figured out.

1. Expose your mysql database to port dokku mysql:expose <db_name> <port>
2. Run dokku mysql:info <db_name> Find "Dsn" (DATABASE_URL). It looks like mysql://mysql:@dokku-mysql-staging-db:3306/
3. This URL contains all the information you need [Database type]://{username}:{password}@{internal docker host name}/{db_name}
4. Now you can connect remotely to the database GUI

I successfully connected using Sequel Pro and the following information was displayed:

Host: { your servers IP address }

Username: { username from DB URL }

Password: { password from DB URL }

Port: { port you exposed the DB on }

PS: I read somewhere that you need to disable UFW on the server, but I'm not in server administration so I don't know the consequences of that.