refreshing combox after closing form c#, win form

I just wanna refresh a combo after closing the form...

I got this...

private void btnBtn_Click(object sender, EventArgs e) { frmCat frm = new frmCat(); frm.ShowDialog();

}

When I open this form, the data inserted on it, I wanna show it on the first form after closing (I wanna show it on cmbCat combox)