Go to Vehicle Management > Fuel Tax. Find the unit that has the incorrect fuel tax trip via search or one of common views.
Click on the unit code to view the list of fuel tax trips for the unit. Click on the trip number.
When viewing the trip, select Change Trip - Unit on the left.
Enter the correct unit code in the box, or use the spy glass to the right of the unit code box to select the new unit. Click Save to move the trip to the correct unit.
If additional trips need to be moved, repeat the process above until all trips have been moved to the correct unit.