This guide will let you know how to activate your Hunter’s arm in the wild heart so you can get that mission done.
You will find the glowing green spots, they’re the weak ones, so you need to jump up and press R1. Just grab onto the creature from the green spot and use your Hunter’s arm with L2. It’s a right trigger, left trigger on Xbox.
You can climb anywhere on most of the Beast if you find the vines. Climbing on them and jumping right where the green spot is easier. They will get knocked over when you break all of them.