What is it?
Overpronation is a problem that occurs when the ankle rolls inwards and the arch of the foot flattens. It is widely known in the running community and is widely assumed to be associated with a number of different running injuries, though there is a lot of debate about that. Overpronation has also been the basis in which running shoes are often used, though there is a lot of debate about that as well! Overpronation is not always a problem and there is a lot of misunderstanding about it. It can be associated with an abductory twist.
How to manage it?
As overpronation is not always a problem it does not always need treating. If it is contributing to a problem that you have, then yes it needs treating. The problem with overpronation is that there are many different casues, so there are many different treatments. The first line approach is to use supportive shoes and inserts.
When to see the doctor?
If that does not help, then you really need to see someone who knows enough about pverpronation to determine the casue, so can advise the appropriate treatment. Fpr some people it is muscle strengthening; for others it is foot orthotics; for others it is strecthing; and for others it is a more minimalist approach to running. To blindly apply one treatment ahead of another without determining the cause is just plain silly.