How to update a field in a record with a field from a record picker

Hello,

I'm making a custom page for users to link a game session (record) to a player's game session field.

I have two record pickers. One for the Player, and one for the Game Session. For the player selected in the Player Record Picker, I want to be able to assign their Game Session field the value from the Game Session Record Picker. I have added an update button and created a set action, but it's not a dynamic field. I cannot use the value from the Game Session Record Picker.

How can I achieve this?