There is only one way to treat a calcaneal stress fracture and that is to get off it. You have to rest, you have to stop running or stop what ever activity you were doing that caused the stress fracture. If its really painful, you may even need to go into an immobilization boot (walking brace, moon boot). Find some other activities in the mean time to help maintain your fitness, but avoid weightbearing. Keep your fitness up by cycling or swimming.
Thats the easy bit. Once the pain has settled which can take a few or more weeks, the hard bit starts. You need to start back with your running or weightbearing activity and be guided by any symptoms. There needs to be a very slow increase in levels and intensity of activity. If you don’t take this easy as well as slow and steady, there is a very high chance that it is going to happen all over again. The recurrence rates for calcaneal stress fractures is high. You need to plan for at least 2-3 months before getting back to full activity levels. Loads need to be slowly and gradually increased over that 2-3 months. There should be no short cuts here.