The combo box must have all the fields which you want to populate in forms fields. Display the value you want to show in combo box and hide the other fields. Then in the AfterUpdate event of the combo box write the below script for each field.
formfield1 = form.comboboxcontrol.column(column number)
Ex: Combo box has customer information, like
customer name, add1, city, state, zip. The combo box name is "CMBCUSTOMER".
You want to show customer name in the combo box for selection, hide the other columns.
Then the script will be
Me.name = Me.cmbcustomer.column(0)
Me.add1 = Me.cmbcustomer.column(1)
Me.city = Me.cmbcustomer.column(2)
and so on. The column index will always start from 0.
I think this will help you.