Bro did you meet the keldeo in the in the Wastelands? If no, then meet him in the Wastelands you can find him in the South direction after talk to Keldeo kill the Pokemon: Garchomp, Tyranitar, Typhlosion, Zangoose, Flygon, Metagross, Absol. After killing these pokemon you need to talk Noctowl in the south east after the bridge go right side and talk Noctowl there. Then Go right side where you killed the Metagross and Kill the trainers there (They are too much Strong you need the Mega Banette to kill those Trainers) after killing them take some pokemon in your team with certain weight:
1 Pokemon with weight: 100kg - 199kg [Recommended - Goodra or Kingdra (Any Level)]
1 Pokemon with weight: 200kg - 299kg [Recommended - Gyarados (Any Level)]
1 Pokemon with weight: 300kg+ [Recommended - Snorlax (Any Level)]
You can take any pokemon if you don't have any of them but don't forget to take the right weight pokemon (It can be trash, epic, any level) They won't take your pokemon. After clearing those trainers put these pokemon in the given place as follows:
Okay so after completing this part feel free to tell me here I'll be here to help you out of this quest.
Also if you are already done with this part so let me know till which part are done with....
Good Luck!!!