To tame one of these creatures, you would need berries or crops. The best is just Rockarrot. Approach one with the feeding item on the last item slot. Feed it and ride it. You'll need to press the action button (E for PC players) for everytime they stopped moving or the icon on the right flashes, prompting you to use it.
To get a 100% taming efficiency on this creature, avoid spamming the buttons and carefully timing your action button. Make sure that your surroundings are clear and there are not too many threats. They often run off into random areas that tends to be near a Giga territory.
They often spawn in large open fields so that is best to look for one. Good luck and have a good one.
Run run run, crouch when close still approaching at an angle, when close enough,(stack of carrots in zero slot) click three “e” three times; one to feed, one to mount, one to start THE RIDE! Each time you get the feed prompt, hit “e” and pray it gets stuck in a corner and doesn’t run off a cliff, or into carnivores. Ignore everything but the prompt, hitting “e” without hesitation. (You cannot control the run at all). That’s it.