In order to redeem your loyalty rewards, you will have to log in to your account.
Once you are in your account you will find your loyalty reward points in the "My rewards account" section. You will have the option to transform your loyalty reward points in a voucher by clicking on the button "Transform my rewards into a voucher".
The voucher will give you a code that you can apply at checkout, in the "Vouchers" section.
All your Vouchers are stored in your account in the section "My vouchers".