Final Boss help, can you exit the battle to get items?

Hey I'm looking for help for my kid who just got it for Christmas, he's having trouble (possibly underleveled) with hyperrogue ange floette, he said when he leaves the battle area all the centers are closed, is there a way for him to basically exit the battle so he can level up more or go buy more items? Sorry for possibly a dumb question, I can't help because I don't play the Pokemon games, so any help would be appreciated, I googled around and couldn't really find a good answer as to whether this is possible.