Go to the Security section in your Gmail account and make sure Two step verification is turned on.
Log into the user’s Gmail account and select the Google Apps icon located in the upper right hand corner of the screen. Next, select Account.
On the left hand side, select Security.
Move down to 'How you sign in to Google'. Click on 2-Step Verification and turn it on.
After you turn on 2-Step Verification, you will be able to generate an app password for Tres. Enter "App Password" in the search menu of your Google account or follow this url to generate an app password: https://myaccount.google.com/apppasswords.
Enter Tres as the App Name and click Create.
Copy the app password, and paste it in the password field in Tres.