How to refresh the combobox from one form in another

Hi,
I have a form with combobox. I want to enter a new value in the combobox form another form

In the second form I have:
 private void button1_Click(object sender, EventArgs e)
  {
  OleDbCommand com = new OleDbCommand();
  com.Connection = conn;
  com.CommandText = "Insert into Komin ( Komin) values ( ?)";
  com.Parameters.AddWithValue("@Komin", textBox1.Text);
  try
  {
  conn.Open();
 
  OleDbDataAdapter oleDbAdapter1 = new OleDbDataAdapter(new OleDbCommand("Select * from Komin order by ID asc", conn));
  com.ExecuteNonQuery();
  dataset1.Clear();
  oleDbAdapter1.Fill(dataset1, "Komin");
 }
  finally
  {
  textBox1.Text = "";
  conn.Close();
  }
  button2.Focus(); 
  }
so, I enter the new value and I can see it in the access database. But when I close the second form I can't see the inserted value in the combobox, until I close and reopen the form. In the first form I have:
private void button11_Click(object sender, EventArgs e)
  {
  Komint komin = new Komin(this);
  komin.Show();
  }


to open the second form for entering the new value.

What can I do to refresh the combobox in the first box on clicking the close button in the second form?
Now I have:
 private void button2_Click(object sender, EventArgs e)
  {
 
 dog.Show(); 
  this.Close();
  }
but if I put this code, two windows are open for the first form.

Please help me if anybody has an idea.

Thanks in advance