Your check box is bound to a table field so you need to run an update
query:
CurrentDb.Execute "Update MyTable Set MyTable.CheckName = 0;",
dbFailOnError
You will need to have a library reference set to the
Microsoft DAO 3.6 Object Library.
Open any code window. Click on Tools + Reference.
If you already have a reference to the above library set you don't
have to do anything. If the reference is not checked, scroll down the
list until you get to it. Place a check in the check box. Save the
change.