Step 2:, make thief 1 tie up thief 2, under the threat of shooting them.
Step 3: make thief 1 tie up his legs and put his hands behind him.
Step 4; put gun next to you and tie the hands of thief 1.
Step 5: make them hop on your quadbike.
Step 6: drive into a police station and get arrested.
I think the "correct" thing here would've been for him to keep them at gunpoint while waiting for the police to arrive to arrest them. Citizen's arrest are a thing, but hogtying people and making them ride on your quadbike like that? Unnecessary.