The hard part is finding one. K.Oing one and the whole taming process is easy. Bring lots of narcs and kibble. It's recommended to find one first before bringing your kibble and narcs in case you get killed.
Center tip: as they have added the mosa to the center I've found the easiest way to knock one out is find one close to the bubbles get its Agro and swim in the bubble the mosa will get stuck and it can't hit you. Also this gives you unlimited oxygen and sanctuary from being attacked by anything else. ðŸ¤˜ðŸ¼