While you're viewing the wolf, look at the companion section. You'll see a little pencil in the top right corner, click that and then you will see an option to remove companion ^.^
Edit: I am so silly for forgetting to add what bonibaru said xD I'm sorry, I hope I didn't cause you frustration!
What nikki said, but also you can only remove a companion that is not on cooldown after being played with. You will have to wait for their cooldown timer to reset to 0.
