There are more possibilities to hike up to the Gamshütte (1921m):
From Finkenberg to the Grünberg-Alpe
From Ginzling (Zemmgrund) to the Saustain-Alpe
From Tux from the Rosengartenbridge over the Grünberg-Alpe over the Els-Alpe on the Rudl-Stöckl-Weg
The following description is from the Hermann-Hecht-Weg:
You go by bus or by car to Finkenberg. Then you walk over the bridge and turn right. Walk along the route till you see the football ground. Here starts the trail to the Gamshütte. Walk along the forest road which goes always through the forest. After 1,5h you come to a little hut. From here you have a wonderful view into the Zemmgrund! After 1,5h you get to the Gamshütte (1921m). The last increase is a little bit steep.