The next page of our Assassin's Creed 3 Remastered guide contains a walkthrough for Alternate Methods.
To begin the mission, head out to meet with your father in New York.
After a short cutscene, run after him until you reach the rendezvous point of British officers. You need to exactly follow your companion, so that the nearby guards don't detect you.
Optional objective: Use guards as human shields - 2/2.
As you reach your destination, jump down and start the fight. If you want to complete the optional objective, initially focus on dodging enemy attacks and wait for the officers to use firearms. Press the jump button by the nearest soldier and use his body to block the shot. Do it twice to complete the objective.
Optional objective: Tackle the target from above.
Optional objective: Complete all optional objectives during a single playthrough.
With the last enemy killed, you will have to chase the officer. In order to catch up with his fast, don't follow him into the narrow alley but instead run forwards all the way. Turn right only after reaching the big square and wait there for the officer.
As he shows up, let him overtake you by a couple meters and afterwards run to him and press the attack button to knock him down to the ground. Remember to have fists equipped.
In order to obtain full synchronization, you need to overtake your enemy by a couple meters and afterwards turn right and then left.
In the narrow street there will be a laundry string. From there you can jump down onto your target. However run up only when the officer is nearby, or you will be shot down by the guards.
After catching the man, lead him to the fort by pushing him with the jump button. The mission will end there.