How can one treat a heart murmur?

Depends . On the specific murmur. Some are physiologic and benign while others may be pathologic. See your doctor.
Why do you ask ? A murmur is just the sound of blood flow. It can be murmur bad=sign of a problem that needs help, or murmur good= nothing of any importance. If I listen to a patient often enough in their life I expect to hear an innocent murmur at some point. The ones that are not would vary in their treatment based on the problem it represents.