If the combo is a bound field, in the close event for the adding form, try Forms!frmFirstForm.Requery.
If it is not, you'll have to drill down to the actual control: Forms!frmFirstForm.cmbComboboxName.Requery
Sub in your actual object names.
You may want to ensure that the first form is still open, otherwise an error will occur when trying to requery a form that is not open.
Code:
If CurrentProject.Allforms("frmFirstForm").Isloaded Then
Forms!frmFirstForm.Requery
End If
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.