I do the same thing as a result of weak knees, it's painful to turn them in but if yours isn't an issue like that I'd just recommend trying to grab with your calf rather than your heel and make a conscious effort to turn your toes in without pinching with your knee. They don't need to be perfectly straight forward because that's ridiculous but if you constantly remind yourself it should form a habit. If it is due to joint pain then physio and corrective exercises are your friend