The Arena is a battle-focused area in Pokemon games. It's meant for battling trainers and participating in competitions, not for catching Pokemon.
To catch a Bellossom, you'll need to find it in the wild and use Poke Balls. Here are some ways to do that:
* In Pokemon GO: Bellossom is a Grass-type Pokemon that evolves from Sunflora. To catch a Bellossom, you'll need to evolve a Sunflora using a Sun Stone.
* In other Pokemon games: Bellossom is typically found in grassy areas like meadows or forests. You can also encounter it in specific locations like the Safari Zone or certain routes.
Remember, it's important to use the right Poke Balls and items to increase your chances of capturing a Pokemon. Good luck!