Sunny,
var gr = new GlideRecord('sys_user');
//The below query will reset the password for all users whose date of password is dated more than 20 days before.Change accordingly.
gr.addQuery('u_date_of_password','<','gs.daysAgo(-20))');
gr.query();
while (gr.next())
{
gr.password_needs_reset = true;
gr.update();
}
