I want to run a schedule function daily that if certain criteria is met, a field in that deal gets updated.

I have a date field "Last_Day_of_Coverage". If the date in that field is exactly 90 days from today, I want the scheduled custom function to update another field "Has_User_Renewed_Policy" to "In Progress" on that deal.

I have previously worked with Deluge, but it was always from within a record. I don't know how to make a custom function check all the records in a module to evaluate if a specific field has a specific value. Any help would be appreciated.