Dissolve the contents of the required number of capsules (one capsule per 1.5 to 2 liters of milk) in soy milk pre-heated to 42°C. Stir well until the starter culture is fully dissolved. Pour the cultured milk into prepared containers. Leave to coagulate at 42°C for 6 to 8 hours, then at room temperature for approximately 2 hours, and finally refrigerate for 8 hours.
See the detailed guide here.
The quality of the finished yogurt depends on the quality of the fresh soy milk you use.
If the result is unsatisfactory, try a different type of soy milk.