Saved Search for the Absence of a value?

I have a custom check box field Holiday Gift {custentity_holiday_gift} on the Customer Contact record.

I have historically needed to know a list of Customers where no Contacts have this box checked and have used a "Customer" Saved Search with results as:

Formula (Numeric)>Summary Type = Count, Formula = DECODE({contact.custentity_holiday_gift},'T',1,0)

Now, 🤔We want the Sales Rep to determine and update:

of these Customers, that have no Contacts with a Holiday Gift {custentity_holiday_gift} designation, mark one of the contacts Holiday Gift = Yes.

The way the search started out, since it is a "summary" search AND from the Customer record, the Sales Rep cannot "in line edit" the list to update the Holiday Gift {custentity_holiday_gift} field check box.