C# :: Selection From 1 Form DatagridView On Second Form

I have 3 Windows Form: frmMain, frmFirstForm, and frmSecondForm.

frmMain is the form that will load when the application is started with 2 tabs to access frmFirstForm and frmSecondForm.

Here's my problem:

After making a selection from a combobox on frmFirstForm, I would like a datagridview header to change based on the selection made. Here is a list of items on one combobox: Item1, Item2, Item3, Item4. When somebody chooses Item one, the header on the datagridview on frmSecondForm should display: JohnItem1, PaulItem1, BradItem1 and so on. Those items are not part of the comboboxes, but they will be shown as header text on the datagridview on the second form either automatically or after clicking OK from frmMain. There's no OK button on frmFirstForm, but on frmMain.

The only code I have right now is the if statement on the form load on frmSecondForm. Here's what I have:

private void HeaderTextLoad() {
if(comboboxonfirstform.text = "Item1") {
datagridview1.Columns[0].HeaderText = "ItemJohn";
datagridview1.Columns[1].HeaderText = "ItemPaul";
... And so on.
}
}