He already knew he could. He budged it during Avengers Age of Ultron, and he probably would have noticed it move (Thor did). But he stopped trying so he didn’t embarrass both himself (by claiming to be worthy of godhood when he’s a pretty humble guy) and Thor (by being just as good as him despite being mortal).

So, when the opportunity came again, it was a no-brainer. He knew he could, and he knew it’d be useful to him.