TurboTax accounts cannot be merged or combined. Abandon one of them and stick with the other one going forward. Keep a record of how to access the "old" one in case you need to look for an old return, etc.
Link your TurboTax account to Credit Karma
https://ttlc.intuit.com/community/intuit-account/help/is-credit-karma-a-part-of-turbotax/00/2092900
https://support.creditkarma.com/s/