[Koha] Hoilday delete function not working in Koha 3.12

I made mistakes in setting the holidays in the calendar under Tool. There is an item for deleting a single holiday. However, After I put a dot in the circle next to the that delete item and saved, there was no reaction. Is there any way to get the deletion done? Or is there any where on the screen has the solution that I have missed? Thanks. Hing-choi