First, be sure the email is not ending up in your spam/junk folder. Then try this:
Near bottom of left column menu go into Intuit Account. Then go to Sign In and Security. See if your email address is correct there, and if so see if it is "verified." If not, you can verify it there with the link there It may then send you a link to that email address to verify with. Once verified for the Intuit Account purposes, close Online TurboTax. And then sign in again.
That might be enough to fix it. When you try to efile, if it still wants to send you a 6-digit email verification code, be sure the code is not ending up in your email's spam/junk folder or another email address you have. See this FAQ on some tips, which also includes info on how you can change the email address in your Account Settings, if you wish to use another email address.
FAQ: What if I'm having trouble with my filing verification code?
If that's not helpful, please phone Customer Support.
Support hours are 5AM-9PM Pacific, every day this time of year.
FAQ: What is the TurboTax phone number?
https://ttlc.intuit.com/community/using-turbotax/help/what-is-the-turbotax-phone-number/00/25632