PostgreSQL doesn't have a merge function so to have the same database for both machines you'd need to import into each of the databases those hands only the other one has. You can do that by importing from your
processed folder and/or
exporting hands. To manually processed/exported hands select "Get Hands From Disk" after clicking "Play Poker". Depending on the number of hands you have this import may take some time. You therefore would want to schedule this to start at the most convenient time. In other words I would not start this import if you have important poker sessions coming up as you cannot import manually and use PokerTracker 4 on live tables at the same time. If required you can break the import up into smaller chunks/folders. Once the databases have the same data you could keep them in sync with something like this:
Guide: Syncing Hands Between Two ComputersIncidentally if one of the machines is always on even when not playing poker from it then there is a further option available where you can have both machines sharing the same PostgreSQL/database so no matter which computer you play from:
Guide: PostgreSQL Server Hosted on a Local Network