Is use a taming raft with a ramp and a basic wood ramp parked behind. Aggro on a bird and lead into taming raft. Land bird on basic raft just behind and shoot arrows from it. Sometimes with taming rafts rexs can still get the occasional nibble on you hence the second raft. I take them back to my base near swamp and farm paracer for prime.
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” 👌😄👍
Don’t be afraid they are really slow, just get some raw prime, a crossbow, narcotics and some tranqs and go for it. good starter tame you can have follow you until lvl 70 when you can ride it. also very good for bosses if you have ascendant saddles and high levels