Seveal ways...
First and most straight-forward would be to hard-code a value in the "Initial Value" field in the "Advanced" properties of the combo-box object.
-or-
At some point in the code - like on load of the screen or on refresh or in a clear-fields procedure - just set the "screen-value":
cb-name:SCREEN-VALUE = "default value" - assuming that value is in the "list-items" of the combo-box.
-or-
You can always default it to the "first" entry using:
cb-name:SCREEN-VALUE = cb-name:ENTRY(1)
I HIGHLY recommend you use the LIST-ITEM-PAIRS when ever possible (I think that's specific to V9 though?).
HTH
-dk-