Trying to import data to postgres but get permission denied


I am new to I am trying to follow the instructions to upload a data dump to the postgresql database main. I am using the documentation example:

platform sql < my_database_backup.sql

When I try it gives me permission denied. when I try and create a new database I get permission denied.
I can’t see what admin user I would use to gain access to any of the postgresql database.
Thanks for any help on this.