The most important part to focus on, is the left half side, additionally attaching files and adding notes can also be very important, including flight itineraries.
As per the details of creating a Leave Request, these main items shown on the left are the items to edit.
Step through the items on the left as required, updating dates and times, transport, hosts, late meals.
Attach files and update the General Notes as required.
Once you have completed your edits, check the details are correct.
Click Save and confirm the pop-up. All done

NOTE: Updating Leave Request details in most cases will restart the approval process.