If applicable please make sure all elements of any previous PostgreSQL installs have been removed before reinstalling it. To do that you can follow
this tutorial. Next you should manually download and install PostgreSQL v9.3.15
from here. Using a Mac administrator account or administrative privileges install that PostgreSQL and for the password boxes use "dbpass" (no quotes) which is what PokerTracker 4 uses by default. Once PostgreSQL installs successfully reboot your computer and then try PokerTracker 4 again.