When an employee submits their expenses it is automatically recorded against the office they work at. If you are submitting an expense on behalf of one of your employees, you do not have to add their office, this is all done for you.
If you want to be able to see or download a report on each office, e.g. for payroll, then simply click on Expenses in the left-hand column on your Dashboard
This will take you to the Expenses page where you can filter your searches by office and dates and then export a report to send to payroll or add to your files.