I need some clarification regarding an expense. How would I communicate the same to the submitter?

To have any sort of communication to the submitter you can comment on the particular expense within the report. To comment:

1. Go to Approvals on the left sidebar.
2. Navigate to the Reports tab and click the report for which you want to add comments.
3. Under the particular expense, click the Comment icon on the right side.
4. Add your comment in the given box and click Send.