You can tame the Ice Titan by shooting it's corrupted spots on it's body. Keep on doing this for a while until it falls down. After it has fell, walk up to it and claim it. (A claim option will appear like when you imprint on a baby.) I reccommend a good AR for this and some friends help. Solo isn't possible. Happy taming!
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