How can Admin login while Read-only mode is enabled on multisite?

Yes I am using multistite.

I tried with the name of DB ‘secondforum’:

root@localhost-app:/# RAILS_DB=<secondforum> rails c
-bash: secondforum: No such file or directory

Would you provide any example of <NAME_OF_THE_DB> ?
I followed Multisite configuration with Docker
I made it with secondforum instead of b_discourse