First of all, read the letter carefully to make sure this is not a scam asking you to log into a site to share info for them to steal.
You can confirm your return has been accepted/rejected here: https://turbotax.intuit.com/tax-tools/efile-status-lookup/
If your return has been accepted, and you e-filed, then you already provided the correct AGI and you can disregard the e-mail you have received about the AGI.
Additionally, you can check on the status of any applicable refund here:
https://ttlc.intuit.com/browse/refund-status-support
