Here it is:
UPDATE tbl_UserHeader INNER JOIN tbl_UserDetail ON (tbl_UserHeader.Supervisor = tbl_UserDetail.Supervisor) AND (tbl_UserHeader.ClockID = tbl_UserDetail.ClockID) AND (tbl_UserHeader.LoginName = tbl_UserDetail.LoginName) AND (tbl_UserHeader.DB = tbl_UserDetail.DB) AND (tbl_UserHeader.UserGroup = tbl_UserDetail.UserGroup) SET tbl_UserDetail.[Action] = tbl_UserHeader.Action, tbl_UserDetail.Comment = tbl_UserHeader.Comment, tbl_UserDetail.DateModified = tbl_UserHeader.DateModified, tbl_UserDetail.TimeModified = tbl_UserHeader.TimeModified, tbl_UserDetail.UserModified = tbl_UserHeader.UserModified
WHERE (((tbl_UserDetail.LoginName)=[Login name]) AND ((tbl_UserDetail.DB)=[DB name]));