As a Controller, you can view all unsubmitted expense(s) of the users that are assigned to you. If you would like to send an email reminder to the users about these expenses you can follow the steps as written below. 

Send email to the involved users

1. Go to the Expenses overview.
2. Switch role from Personal to Controller.
3. Select All (next to To Do).
   
4. There are 2 ways to remind a user
   1. Select the expense you want to remind a user of by selecting it, and click Actions on top of the screen. Choose Send reminder.
      
   2. Open the expense by clicking it, and click Send reminder on the bottom of the expense. 
5. A confirmation message will show up at the top of the screen, once the email is sent.