Unfortunately, there's no way to edit a recorded drive! You'll need to delete the incorrectly recorded drive and then manually add in the drive with the appropriate mileage.
First, delete the old incorrect drive:
1) Select the incorrectly recorded drive from your Deductions screen
2) Tap "Edit" from the upper right-hand corner of the screen
3) Tap again but on the three-dot menu in the same upper right-hand corner
4) Select "Delete" from the dropdown menu
5) Confirm deletion
And then manually add the correct drive:
1) Click on the green "+" button on the home screen or the one located in the bottom right-hand corner of the Deductions screen
2) Select "Add Expense"
3) Select "Add Miles Manually"
3) Enter your actual mileage distance, date, job category, and any notes
4) Tap "Save"
After you follow these steps you'll be up to date with the correct mileage!