I accidentally created a second account this year. How do I merge my accounts so I have one account with all of my tax returns? Thank you!

No, unfortunately there is not a way to merge two accounts. If you have not purchased and filed on the new account, I'd clear and start over from Account settings and let that account go dormant. This will clear all of your tax information but it will keep your personal information. No worries though, TurboTax is very serious about their security.