Get lots of diplodocus and level up nothing but health and also put saddles on them all have them attack the titan. The titan will be distracted and the diplos won’t do any damage. As he’s distracted use the time to destroy the corruption spots. Once all three are down walk up and claim. There you go
Pro tip: Don't use explosive weaponry and really bad rexes with no saddles like the devs did. Fab Snipers for taming it with little/no collateral damage, actually decent rexes + imprint + saddles to kill it
Try to hit the coropted glowing things around his body. Ice you have destroyed all, it should fall down on the ground knocked out. You do not need any taming food for it, Just go up to it and click tame to tame it. No need to build a saddle because it already comes with one.