Ive heard/saw on youtube that you can just jump off your argentavis or any other of your tamed flying dinosaurs and land on the wing of thw wild quetzel. make sure your bird is following you to. You can then just shoot it in the head till it knocks out. Make sure you have a parachute with you just in case you miss the bird.
The fun way is to jump off and grapple to your argie and whistle it to attack and since argies are slow it won’t catch up in time so tranq till it goes out also bring parachutes and consider liking so more people will know
In order to solo tame a quetz, you could use an argentavis and a pulmiscorpius. Just pick up the pulmiscorpius, and do whistle attack target while looking at the quetz, your pulmiscorpius should start attacking the quetz, raising it's torpidity until it is knocked out.