To redeem your League of Legends Gift Card, follow these steps: 

1. Open your launcher for League of Legends.
   
2. Click on the Store symbol in the upper-right corner. 
   
   
   
3. Select Purchase RP. 
   
   
   
4. Click on Prepaid Cards and Codes 
   
   
   
5. Input your Key and submit. 
   
   

(Check the region before redeeming a gift card because they’ll only be applicable to those regions/countries.)