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.