As Administrator you can see all the reports and expenses of all Submitters, you are able to check the expenses and see if something is missing.
Via the All Reports overview and the Unsubmitted Expenses you can see all the expenses but you are not able to change anything. If you would like to change things you need to click on the 'Approve' button or the 'Export' button. You need to have those rights tough.
You can also add yourself as assistant to the Submitter you would like to help and change the expenses via the assistant function. How to set the assistant function you will read here.