If you want to utilize a welcome offer, you can find this feature under Account>Settings>Offers.
Once there, you would need to enter your affiliate referral code within the first 24h upon account creation.
*Please note that in case your account is older than 24h, you will no longer be able to manually enter the code. Anyhow, if you used a referral code to create your account, feel free to contact us on Live chat and ask about this. We will help you further with it.
If you happen to have any further questions about this, feel free to reach us out at any time.