You set them.
Based on what you posted you have an Actor class that is your loot table. That class has a variable “Loot Table” that’s a struct.
Typically you’d simply drop one of those actors into the level and set the values, then save.
In the game mode: Begin Play -> get all actors of class (loot table) -> get (index 0) -> Get Loot Table -> Set GM Loot Table variable. Then reference the GM’s loot table var for all future processes.