https://support.riotgames.com/hc/en-us
click on submit a request and follow the steps from there.
You'll vhav to choose a category, fill in your info such as email, username and ingame name and ofc. your question
If all the info is correct, at 1st you''ll get an automated email saying that your request has been received but will take some time because of limited staff etc.
a riotet will respond and help you sooner or later but shouldn't take more than a few days.
In case you get an automatic auto response after waiting a few days just click in the same email that you want your ticket to be reviewed by a real person. and things should be good.
glad to help ^^