You will only have a "Ground Consumption" option listed in the fuel tanks loading window if you have a ramp weight limit set up on the SETUP page.

Image 1.  A W&B profile with no Ground Consumption field.

To set up a ramp weight limit, open your W&B profile and go to SETUP > WEIGHT LIMITS and tap on RAMP.  Enter a weight in the Ramp field.  If you do not have a published limitation, simply enter a value equal to your Maximum Takeoff Weight.

Image 2.  Enter a maximum Ramp weight.

You will now have a Ground Consumption field listed under your fuel loading section.

Image 3.  You will now have the Ground Consumption field.