Hello, the AGI transfers over automatically for all returning TurboTax Online users. If there are issues with it being accepted I would check and see if you're in the same account as last year. Here's the account recovery tool to find any other accounts you may have, just be sure to log out of any open tabs: https://myturbotax.intuit.com/account-recovery/
If that's not it, did you amend the return by chance? If you did, try using the original AGI amount that was transmitted to the IRS.
Also if you have a spouse, make sure the amounts for the AGI under you and your spouse are the totals. Don't split up the AGI between each other.
I'm also posting an article below that helps confirm the AGI location to make sure you have the right amount, just in case:
https://ttlc.intuit.com/replies/3301618