You may login to your account and visit https://www.casetify.com/user/settings, then edit your birthday in the "Month Of Birth" field, and click "Update Settings".
Each member is allowed to update the month of birth once.
You may use the Birthday Gift offer within 365 days of your Qualitying Purchases as a Silver Tier Member. You may log into your CASETiFY account, go to "Rewards" under "My CASETiFY Club", and you will find your valid vouchers and gifts there. Alternatively, you may check the Voucher Wallet in your shopping cart after logging in and adding your desired products in the shopping cart.