Hi mrnobody,
Click on the blue Program-Buss icon and then where you see Fretless B15 at the top of the list, further up you will see a little grey box saying FX.
When you click on that box all the effects will appear so click on one and then click on the Edit tab in the main window of Halion 5 where you can adjust the effect to taste. If you want another effect click on the little grey FX box again!
Hope this helps?
Kind regards
James Colah