How can i get free skins (Medieval Twitch and Grey Warwick)

I want to know, how can i get the Twitch and Warwick for free. I see on a site: To Unlock the Grey Warick Skin and the Warwick Champion if you don’t own him already. You Need To Have 3 Friends, Level 10 or higher in the refer a friend program. How cen i get the "refer link" ?
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