When you're given an access voucher - it doesn't matter if you already have an account or not - head on over to https://www.chinesepod.com/redeem and fill in your information. If you already have an account, we'll ask you to log in first before applying the voucher.
HOWEVER! Please be careful if you already have an active ChinesePod subscription. ChinesePod doesn't support having multiple subscriptions or allowing one subscription to extend the other. If this is your case - please reach out to firstname.lastname@example.org and we'll help you solve it.