-Visit minecraft.net/redeem. Then folow below steps
1-Input your 25-digit code in the “Enter Code” box.
2-Sign in with the Microsoft Account in which you would like to use the item.
3-Follow the instructions to download the item.
4-Go to My games and Apps, or My library on the device you play Minecraft on, to download the item.
5-Enjoy your item in Minecraft