Question

How do you do OU,Ubers,UU,RU and NU Wi fi battles ?

Answer 1

You cannot. The Smogon tiers system is merely fanmade, Nintendo or Game Freak have not implemented them in the games. However, if you are batteling a friend or another person using the Friend Codes, you can communicate with, you can decide if you are going to use a certain tier.
But there is no way off batteling in a specific tier in Random Matchup, PWT or any other ingame battle so to say.

Comments

yes but,The youtube user The Pikawu has done ou,uu etc wi fi battles

---

He probably use Pokemon Showdown, Pokemon Online or Smogons Wi-Fi Battle Finder.

---

No Flaaf he is playing with his real life friends, and just like you said
if you are batteling a friend or another person using the Friend Codes, you can communicate with, you can decide if you are going to use a certain tier.

---

Thx, I just listed additional options

Answer 2

You can't because tiers are fan-made so, Game Freak wouldn't implement them in the games.