How to redeem Riot game card?;

Open the League of Legends application from the icon on your computer’s desktop.

Launch the game, and sign into your League of Legends (LoL) account. Once complete, click the treasure chest icon to go to the Store.

On the left side of the screen, click ‘Purchase RP’

You will see several options for adding funds to your account. Click the ‘Prepaid cards’ option.