From an existing shift, clicking on the blue More Actions button will show the option to Copy the shift.

If the shift is a recurring shift, clicking the copy option then allows you to select whether to copy all of the settings from the recurring shift pattern or just the one-off details for that shift.

A new shift is then created and remains in edit mode, it is not automatically saved (as used to happen with this feature). The same settings as the shift you had copied are entered into the shift for you to adjust as appropriate - all settings can be changed including the staff or client, the date, time or recurrence frequency.