On mobile single player I used about 12 behemoth gateways to make a large pen. Lure titan into pen, place last gateway and tamed with Quetzel/cannon technique. Just go past render distance after each shot and come back and repeat. This was tedious but better than it drowning when it flees.
Don’t try to use rpgs, they don't get it down fast enough and the titan turns around faster than the rpg moves across the sky. When i first tried to tame one it started getting the torpor up then ran into the water killing itself:(