how do I change my level setting from intermediate to beginner

As far as I know, your level setting only affects your starting rating. Since chess.com uses the Glicko2 rating system, your first few games will shift your rating drastically towards your actual playing strength.
You've played five games already. So your initial choice of "Intermediate" no longer makes any difference.

He doesn't.
It doesn't matter. That setting only affects your STARTING rating. His will be unrealistically high at first, but the way that Glicko-2 ratings work, it will change very rapidly in the first few games and quickly drop to a realistic number.
He'll get paired against opponents who are way too strong for him (and get massacred every game), but only for the first half-dozen or so games. By the time he's played 10 games, he'll be paired against opponents of his own strength, and will be winning about as often as he loses.