If you clicked on the link in the email, the discount will be applied automatically when you arrive to the page where you are to pay your TurboTax fees. If you do not see the discount, log out of your account, clear your browser's cache and cookies and log back into your account to see if the discount is applied. If that does not work, we recommend that you try a different browser.
https://ttlc.intuit.com/replies/3302272
https://ttlc.intuit.com/replies/3301745
If none of the above works, then you would need to contact customer support for further assistance.
https://ttlc.intuit.com/replies/3300041