I gave you the code in my reply. But perhaps you are not familiar with how
to put that code into your form?
Open form in design view. Click on the first combo box control. Right-click
and select Properties from the menu. Click on Event tab in the Properties
window. Click in box next to After Update property. Select [Event Procedure]
from the dropdown list in that box (click the combo box arrow at far right
of this box). Click on three-dot button at far right of the box, which will
open the Visual Basic Editor. In that window, you'll see a line of code that
starts with Private Sub, a blank line, and then a line of code that says End
Sub. In the blank line, type this code step (replace my generic
SecondComboBoxName text with the real name of the second combo box):
Me.SecondComboBoxName.Requery
Save the form and close it. The second combo box now will be requeried after
you make a selection (or type a value) into the first combo box.