How do I do this?

Dremel tool with a cutting wheel will make short work of that bucket.. 👊

Hi! Best way is to break the plastic container ands try to transfer as much of the soil clump you can to that pot. If it does not fir you can try to shake some soil off and fit it then! Try not to brake the roots while doing it to avoid too much stress. If you don't want to break the pot you can wet the soil thoroughly to get it to clump and try to slide the whole thing out of the container gently