Most third party companies offering Turbo Tax discounts offer their own specific site to access Turbo Tax which will apply the discount. I would check the email you received with the information containing the promotion, or where you received the information for the discount details. There should be a specific link you would utilize that would then apply this discount. Please see the below article for additional information:
https://ttlc.intuit.com/replies/4652791
[Edited 4/8/19 8:11PM CST]