You can't, it's driven by the airplane refueling point under the wing, the airplane size and where it has been parked.
By default it's enabled if there's a jetway and disabled if the parking is in the open. The program already has an internal way to customize it by parking, but we haven't set an user interface for it, but it will be a reasonably quick addition with a future update. It's all already planned, there will be an "Underground Fuel" flag to enable/disable in the parking customization editor.
