Once you unlock the pack leader ability you will be given the tutorial on controlling your brawlers, including locking onto a target with the left trigger and pressing the right stick button to instruct them to attack.
You can obtain this achievement by attacking parked helicopters. The large base in the Downtown area of the Red Zone, location of a skybridge, contains three parked helicopters. Summon your brawlers and command them to attack the three. You can either wait for a Strike Team and attack them, or leave the base and return after filling your mass bar and attack the parked helicopters again.