How to develop a function that can be called from the 'custom actions' menu to update a specific field in all selected records with a specific value that the user must enter

How to develop a function that can be called from the 'custom actions' menu to update a specific field in all selected records with a specific value that the user must enter

Dear all,

I'm looking for a function to update a specific field in all selected records in a view, with a value that the user must enter in some way. The implementation is to make a function that is called form the 'custom action' menu.

But I'm too low level programmer to see how to do this.

PS, I do not want the default function 'bulk edit'  because then, the users see all fields in the form to update which is unwanted.

Kind regards,

Silvester Draaijer