I'm not sure what they'd be able to adjust, as the alternator drive belt/serpentine belt has a self-tensioner! :lol:
To replace the belt, you need to lift the tensioner with the correct size ring spanner (this provides the leverage to enable you to fight the spring, which is very strong) then swap the belts and relocate the tensioner. I keep a spare belt and suitable spanner in the car in case the belt snaps. It typically takes a breakdown truck over an hour to get to you out here, the spare belt and spanner would have you back on the road in a few minutes.