Resetting the pgadin4 web usto run,er credentials

After getting pgadmin4 installed and configured, I've found out that the user credentials I specified during the setup don't work very well. I've added the user to the postgres db using the adduser command. I updated the pg_hba.conf file with an entry just for the user but I get this error when trying to connect for the 1st time:
FATAL: no pg_hba.conf entry for host " my.dbserver.ip.addr", user "p(at)p(dot)com", database "postgres", SSL off
psql postgres
postgres-# adduser p(at)p(dot)compostgres-#\q

pg_hba.conf entries (actual ip number hidden):
host    all             all             my.dbserver.ip.addr/32 trust    host    all             p(at)p(dot)com         my.dbserver.ip.addr /32 trust    # for pgadmin4 web
So I would have thought the 1st entry would cover all users. I can't create a linux user because the user name is invalid:
useradd: invalid user name 'p(at)p(dot)com'
So to make it work, I'd just like to set the username/password to the postgres user. Where can I do that? I don't see a .py or .conf file other than pg_hba.conf where the user is defined.

Thanks. Kevin