Restoring an Immich Backup

I’m not sure if I’m doing this right, but I’m trying to restore by Immich database in a new Dataset. I’ve tried using gunzip in shell but I don’t know what to enter for the username when I try to launch postgres. I’ve tried a few things it might be but I’m afraid it wants the userid number created when I set up the app the first time and I don’t know how to get that nor do I remember what it was. Also, is gunzip the best way to restore the database in the first place? The documentation seems to be pretty sparse on actually using the back up files.
For the record I am a complete newb when it comes to TrueNAS and my Linux proficiency is low.