crimsonred36 - great you figured it out!
Some Flockport PHP containers already have phpmyadmin, adminer and opcache. It's documented in the Flockport Guide. The Flarum container has all 3, and the microflarum container has adminer.
These are located in the '/var/www/shared' folder. If you have a look at the Nginx config in '/etc/nginx/common/locations.conf' you will see how it is accessed.
It's available at 'myflarum.org/fp/' or 'containerIP/fp' location and protected by basic http-auth and the default user and password is flockport. If you browse to the /etc/nginx/sites-available/flarum' file you will see an include line at the bottom that references the locations.conf file. If you comment this out this access is disabled.
Since you are using the microflarum container it has adminer in the '/var/www/shared' folder. If you prefer phpmyadmin just download and place it in the '/var/www/shared folder'. Now you can access it by pointing you browser at 'myflarum.org/fp/'.
You can change the httpauth password by using any htpasswd utility, in Alpine Linux the apache2-utils package has the htpasswd utility. The password is stored in the '/etc/nginx/htpasswd' file. In Debian containers we usually include a 'crypt.pl' perl utility in the /var/www/shared/folder that can be used to change the htpasswd file credentials.
You can disable this access by deleting the '/var/www/shared' folder or deleting the related config section in '/etc/nginx/common/locations.conf'. It's a good idea to simple rename the /var/www/shared folder when you don't need to access the utilities so there is no access.