If you haven't already mailed the returns then you can switch from mail to e-file by following the directions below that pertain to your software version.
Follow the directions below to switch to e-file when using TurboTax Online.
https://ttlc.intuit.com/replies/5561257
Follow the directions below to switch to e-file when using TurboTax CD/Download software.
https://ttlc.intuit.com/replies/3985787