How to set check box using a custom button

Hello all,

I would like to know how to set multiple check boxes to be ticked when a custom button is pressed please. See image below

I have a child table with multiple bit fields, each bit field is set using a check field, the end users have requested a button that can tick all the fields before the record is saved to save them time. I know you can set the check fields to be on by default but this would mean that the users are not looking and using the checklist.
Richard