TurboTax accounts cannot be combined. Choose one to use going forward and stick with that one. Keep a record of how to access the "old" ones just in case. Online saves returns for seven years when you use online TT.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
Sorry, TurboTax does not have an option to merge accounts. Just use the most current account and let the other one go dormant. You would want to use just one account so when you start a return the prior year information transfer to the current return.