Your employees can swap shifts among themselves. In order to do so, you have to allow this in the weekly schedule settings. 

Now an employee that is assigned to a shift can request a swap. She / he stays assigned to the shift until someone takes over. The swap request will be indicated by the symbol of two interlocking arrows. 

The other employees in the relevant location and the department will be informed about the request via email and can now take over the shift.

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