Delete the entry of a pop-up in a Numbers sheet?

Hi,

I’m using pop-ups in a sheet to make it easy to choose an entry (I touch the cell and a pop-up shows up with 4 choices). However, I need to reuse the sheet after it’s full (about a month). When I select all the cells and choose delete, the underlying pop-up choices are also removed.

How can I delete –or set all to none– the entered data while keeping the pop-up options intact to be used for the next round.

Thanks in advance for any help.