The player’s ID or their database user ID? I’d assume the former, as it looks like the identifier column you’re pulling out in your query is their user ID, right? If that’s not the user ID, then you need to specify the correct column in your query. The link @qq_strike posted would help with that.
A player’s ID is different every time they login. When they login, you’d need to keep track of their user ID and their player ID, using something like a dictionary. Then you’d be able to get which player ID maps to the user ID.
You could even use a StateBag or Decor to store the information on the player itself.