I play on official primitive. And I have tamed 3 of these beasts without loosing a single dino. All you need is a average lvl pleis or Mossi and pump health. Ride the Dino down and stay away from any edges then come to a complete stop and wait until it grabs you. Wait around 2 seconds before jumping off and make sure your dino is set to passive. Swim up to it and feed then swim straight up. Keep going but don't go out of whistle distance. Quick whistle all and watch your dino break free and swim up to you then just jump on and swim up and repeat
Use a Mosa to tame this beast. Let the Mosa get grabbed wait a couple seconds get off feed it black pearls. Have your mosa on follow lowest, swim a bit away from the Tuso after feeding it, when the Tuso lets go the Mosa will swim to you. Repeat until Tuso it tamed. Super easy!
You need two people, one for feeding the black pearls and the other to feed the turtle that is in the grasp of the Tusoteuthis, with sweet vegetable cake for the health and to feed it stimulates berries as well