you can set up backups in the user profile, if you need more info check with your internal Concur Administrator.
@dja_sanofi what @NTS explained will work for future reference. Managers need to set delegates before they go out of office to avoid this exact situation. So, most likely you are going to have to have someone that is an Expense Processor approve the report as they can approve for anyone. Usually Expense Processors are people in either your Finance or Accounting Department. I would start by contacting one of those two departments.