The Tasks tab enables you to make changes to the standard task configurations.  

Delete/Close

To delete a shift from a specific date, click on the corresponding cell. From the menu, click on the Delete button.

A red minus (-) sign will appear in the cell that you want to delete.

(View from the Plan tab)

Add/Open

To open a shift for a specific date, simply click on the grey plus (+) sign in the corresponding cell. The sign will stay green and the cell will have a solid black border to indicate the selected slot.

Do not forget to apply the changes on top of the screen

(View from the Plan tab)