To enable Swap mode, Click and hold on your employee you wish to swap on the weekly schedule page:
Click the employee or the shift you wish to swap with,
This will take you to the swap screen, as seen below:
Click on both employees to select them.
Click swap to complete.
Have in mind that the Swap feature can be also used by the 'Employee view'.
On the 'Employee view' of your weekly schedule
Tap and hold, on the employee you wish to swap, to enter 'Swap' mode
Select the one you would like to swap with
Click 'Swap' to complete.