When beginning your NETFILE process, you'll be met with a screen which will say "CRA NETFILE required information". If you choose to enter your NAC code, you may do so in the box provided before selecting Continue.
To find this code, Log in to CRA My Account and scroll down to the “Tax returns” section. Click “Go to Tax returns details” and click on any Notice of Assessment link. Your Access Code will be on the right hand side, below your address, SIN, and date.
Click on this link more information about NETFILE access code.
https://turbotax.community.intuit.ca/turbotax-support/en-ca/help-article/canada-revenue-agency/netfi...
Thank you for choosing TurboTax.