Frank is inside his club at Fristad Rock - Morning. Equip your Havoc slab and preferably a good shotgun before entering the district. To enter the club, get the ClassPass from the machine next to the front entrance, enter the first door, turn around and hack the antenna above the door then return the ClassPass so that you can use your slabs again. When you get to Frank he'll be behind glass inside a closed off room. Kill all Eternalists that spawn and when Frank leaves the room to try and kill you himself activate Havoc and blast away with your weapons. If Havoc runs out before Frank is dead, hide and allow your power to recharge, then activate it again and continue shooting him. When you kill him while Havoc is active the trophy will pop.