controlling form checkboxes from VBA code

Hello,

I am buliding a form for completing forms. In the main document I use a checkbox inserted from tge form-toolbar, and I would like to have it checked or unchecked depending from the value of a control set on a Form.

example: the checkbox on the document has a bookmark name, which is "checkbox1"

There is a control in the macro which called Option1.
The code is

Private Sub CommandButton1_Click()
If optionbutton1.Value = True Then
ActiveDocument.Bookmarks("checkbox1").......
End If

End Sub

What should I put in the place of ....., if I want the checkbox on the documents checked?

Thank you