Purchases Intuit turbotax 2023 last year and then forgot to do my taxes. Attempting to load the 2023 version in order to complete but it give me error code 606. Fixable?

Error 606 means that the code that you are entering is invalid.  So either the code has already been used or you are entering it wrong or you are entering the wrong code.  If you purchased it from a retailer the code should be on a slip of paper or a scratch off card in the box.  If you purchased the download online then you should have received the activation code by email.

@cmdyck 

what to do if my licence code does not work - giving error 606?  Do I need to go back to my retailer?

Yes, I would return it to the retailer.