The password is whatever was set up at the installation time - whenever it was installed on this machine 'postgres' was used.
The only database listed in the database list is the first one - that second database simply does not exist. You can remove it from the PT3 configuration via the Remove button - there is no data in a database under that name installed on your machine. Do you have your other hand histories? If so, you should be able to reimport them into the PT3 DB database without any troubles.