If you forgot the username and password for your other account, you will have to follow the steps below, to go through the account recovery process so that you can gain access to that account.
NOTE: If you no longer have access to the email or phone number listed on that TurboTax Online account, you will need to fill out an email change request here https://ttlc.intuit.com/questions/1899319
https://ttlc.intuit.com/replies/3302318