GT New Horizons updated to version 126.96.36.199
Adventure Backpack 0.8e22 (better preformance)
Standard Expansion 1.0.68 (fix Party error)
Type in the modpack name (GT New Horizons) or paste the following url into the search box.
Finally, click Install at the bottom right of the launcher after you select GT New Horizons from the list on the left. The launcher will handle everything else!