1. Beat the Main Story: You need to complete the main story of Pokémon Black 2 or White 2, including defeating the Elite Four and becoming the Champion.
2. Reach the Pokémon World Tournament: Once you've become Champion, you'll unlock the Pokémon World Tournament.
3. Enter the "Champion's" Tournament: Within the Pokémon World Tournament, select the "Champion's" tournament.
4. Complete the "Champion's" Tournament: You will need to win a number of battles in the tournament to reach the final battle against N.
5. Battle N: The final battle of the "Champion's" tournament is against N, who will be using Zekrom.
6. Catch Zekrom: After defeating N, Zekrom will be weakened and you'll have the opportunity to catch it. Make sure you have a Poké Ball equipped, and use it to try and capture Zekrom. It's a powerful Pokémon, so be prepared for a tough battle.
Tips for Catching Zekrom:
* Lower Zekrom's HP: Zekrom is very strong, so try to lower its HP significantly before attempting to catch it.
* Use Status Moves: Status moves like Sleep, Paralyze, or Freeze can make catching Zekrom much easier.
* Use Ultra Balls or Master Balls: Ultra Balls and Master Balls have higher catch rates, increasing your chances of capturing Zekrom.
* Save before the battle: Save your game before you start the battle with Zekrom so you can try again if you fail to catch it.
* Be patient: Catching Zekrom may take several attempts, so be patient and don't give up!
Good luck catching this legendary Pokémon!