You need to lure a fish swarm (found deep in the ocean) to a megachelon it will then swarm the megachelon and begin taming. *Note that you don’t passive tame this creature with meat it is false, you can however knock it out but it takes a long time for it’s torpor to rise, if the megachelon takes damage it’s taming resets*

More Megachelon Taming & KO Tips