1. You can enter the mileage travelled in the lower mileage field. However, your Trust may have set a limit on what mileage you can, and your claim may be refused. If you hover your mouse pointer over the red symbol. It will tell you what the will accept above the calculated mileage.
2. Your Trust may have set a mileage limit that it considers to be higher than expected, and this will be highlighted for your manager to investigate. above the calculated mileage that they will consider is acceptable.