Step one get long neck rifle get at least 70 darts get more if your aim is bad
Step two find rex there not that hard to find just go to creater maps on dododex and look for tyranasousas rex and
Step three find a cliff it can't climb start shooting it and it will leave and come back a few times but u should be able to tell if it's coming back for u or not u may have to chase it don't start tranqing if if got low ho or attacking a brouto
Just tamed one I will tell you my experience, so I found one and shot it with tranc DARTS (but tranc arrows work just as well although you need a few more :)) and it kept on getting deststracted by other Dino's which made it not attack me, so after I knocd it out I killed the other animals attacking the unconchis body with my Pump shotgun and gave it raw meat and a couple of bio-toxins and boom I got Rexy I hoped this helps on your next Rex tame
I recommend using a scorpion to tame it, pump all levels into health on the scorpion. Then just attack the Rex but with 10 to 20 seconds in between hits, DO NOT pump anything into dm. Also this is what I use to tame literally everything, and it doesn’t even cost anything. Pls put this up in chat for everyone to go “oh that’s not a bad idea” 👌😄👍
So my experience with this beast was horrifying but I knocked it out it took so much tranq arrows it took 30 tranq arrows and I ran fast with the Brontos because there were lots of dinos with the brontosaurus then it was attacking the other dinos then I shot it a lot then it fell asleep because the thing it was attacking a a tank it was an ankylo so that’s my experience with a rex.