How to get Riot to nerf a champion

Find a pro player.

convince him to start playing the champion you believe to be over powered.

if he wins consistently with it than Riot will nerf it.

I remember when Olaf was a true cancer and it took a pro player to 1v5 the enemy team for them to say.. hey .. we need to rework Olaf.

Remember the Poppy rework. there was a Chinese player i believe that was a monster on Poppy.

Sion got his treatment because of the attention AP sion was getting and probably because of the eye sore he was.

Ryze is getting his changes because lets face it. Faker OP.

AP jungler item was quickly addressed when Overpowered's oriana took it into the mid lane.

that is the true way to get the attention of when something will get changed quickly.