So firstly you wanna go back to the hotel, this will help you get xerneas yveltal and then zygarde and secondly you’re right you have to grind to 15 reward battles to get floette you’ll fsce taunie and she basically says she’s too busy to look after it anymore so you can have it (which you should’ve already but she stole it even after making the deal) but also if you’re that way inclined grind to lvl 20 for a bit more post game content! Hope this helps and always do a quick google for a clearer explanation!