The subject says it all. I need to change the gmail account that todo list is connected to.
Please send an email to firstname.lastname@example.org and email@example.com using the email address that is associated with your Premium account and let us know what other account we should transfer the Premium status to.
If you want to keep Premium on the same account, but just change the email address associated with it, you can do it in Settings -> Account (top-right corner). In the "Authorization" tab you can also link a Google Account to your Todoist account.