From Älvdalen, drive RV70 north until you reach Åsen Power Station. Turn left towards Hedbodarna and follow the road until there is a sign "Särnavägen" on the right. Take a right and follow the gravel road until you see a sign where it says "Stortjärnsåsen" on the right side. Park the car as good as you can, there is no direct parking pocket.
From there it is about 1.5km walking. Follow the snowmobile markings (red cross) & later on there will also be orange markings.
If you only want to walk about 500m then you can drive a bit longer by car instead. Take the next right towards Stortjärn and after about 1km there will be a new gravel road on the right. It leads to a turning plane where the snowmobile mark (red cross) is just straight ahead and up the hill. Stortallen is only about 100-200m away.