2018 Suburban tailgate won't open automatically
 

It won't open or close automatically. I can do it manually.

2018? Should be under warranty.

https://cimg3.ibsrv.net/gimg/chevrol...97a4941de3.png
In my 07 Tahoe with power tailgate, there is a switch up near the sunroof. Its that center button in the pic, the one with the open tailgate symbol, this switch can also kill the power to the tailgate, so if you try to open the tailgate from outside the car it won't open.