"restrained" is actually a debuff put on one of the wolves. You can control which wolf gets the debuff by having the tank taunt one and pull it to where the boss is located. The other wolf (the one the tank didnt taunt) should then be pulled to the wall by the chain mechanic (the wolves share a chain so when one is pulled far away from the wall the other has to go towards the wall). At this point just range the restrained wolf down first.
Edit: I should add that this starts the timer for a mechanic called "time to switch" which triggers the wolves to pounce at you if you dont kill one of them fast enough.