Found one on island south of new snow mountain. Pinned it with a wyver so couldn’t move. Used Dino gates off my hot bar to pen around me. Flew wyvern out of pen. Went in with rockacarrot on my furthest right bar. Fed it with promt button ( y on Xbox) then y again to ride it. Couldn’t get out of small pen. Everytime it bucks it’s back legs press y again to feed and calm. Easy, just where guille to get close and watch out for other Dinos when making pen. Your welcome.
For beginner mobile players, if you happen to come across a unicorn, remember the area in which you found it because come later game, you have to take a picture of a unicorn for a pursuit 👍 I found it once and can’t seem to find it again to take the picture 🤦♂️😔