I already bought Turbo Tax at Costco, my computer was not up to date in software so I did my return online- where do I submit the code that I already paid

You should try to return the TurboTax Desktop CD version to Costco first.

If Costco will not give you a refund you can try calling customer service. The best way would be through the Help window in the upper right-hand corner of your TurboTax Online screen or here.   

This WAS VERY Annoying. Your product DOES NOT WORK with OSX!! How can the leading tax software provider not work with MAC? Furthermore, you do not make it easy to transfer the license to the online version. I purchased through Costco with email delivery for a Windows download. There were no options or indications at purchase. Even if there were, Intuit should make it easy to apply the license key to the online version. All I (and millions of others) want to do is license your product. How, after all these years, have you not solved this issue? I am going to post this complaint all over the internet if I don’t get quick remediation or a refund!