Adding a field to multiple modules

Adding a field to multiple modules

Hi!  I've created a number of custom fields in each of the modules (Candidate, Client and Contact) - this is a feature I really love!!!  My problem is that when I originally created a few of the fields I didn't check the box to include that field on other modules.  When I go in to EDIT that field, I don't see an option to check the boxes once the field is created.  Am I missing something?  Please help...