How do I get action by clicking in a cell in a table?

I have never tried this before.

I am trying to get something to happen by clicking on a cell in a table.

I have some screen captures below.

The first shows the booking screen. The idea is you click on a cell in the "Available Column" and if its blank, it shows "Booked".

The second graphic shows my attempt at getting this to work.

The third graphic shows the code. The key point is message 1 which is a control log and there is no message.

This does not fire. Any thoughts?

Mike