You may use /opt/pbs/sbin/pbs_ds_passwd to change the password for the psql database. The remaining steps that @adarsh outlined are correct.
If you don’t mind starting from scratch, you may also do the following…
- Stop all PBS Pro services
- Delete /var/spool/pbs (the PBS_HOME directory)
- Start PBS and reconfigure the services
Keep in mind, this process will delete all configuration data from PBS Pro and you’ll effectively be starting with a fresh installation. Use this as a last resort.