And what will the button do that simply tapping the check box to select a value does not do?
If you truly need the button, there are two ways to set up that field to perform a script when tapped:
You can enter layout mode, select the field and use button setup to turn the object into a button object. The script performed by this button would then need to both modify the value of the check box field in the same manner as you would if it were a simple check box and then it would perform any additional scripting you need to take place.
Or you can enter layout mode and set up the field with an OnObjectModify script trigger that will perform your script when a finger tap modifies the field by selecting or clearing the check box value.