If it won’t allow you to feed it, knock it out and let it wake up then try again. Most likely due to the fact someone else tried to tame it before. Also, it tells you when to feed it at the bottom corner of your screen.
If you want to find you I did.it will be in the redwoods and the beware of the"..........SWAMP!!....but if you see one and you have carrots 🥕 and if it runs away get on it! Hint: you can make it.......JUMP!!! I’m a YouTuber!!,I’m SCHWALBE!
In my single player(mobile) game i found unicorn for the first time in redwoods behind the redwood mountain i killed it and took the implant to revive it cause i hadn't the griffin kibble at that time mine was lvl 20 it just took 10x soothing balm and one griffin kibble.