See below. If you have normal levels, other than moving to a significant altitude there is not much more you can do. Taking additional iron, B12 or Folic Acid will not help, as red cell production is tightly regulated. If you have anemia, however, a proper diagnosis maybe need. The most common cause of anemia in the world is iron deficiency, but there are other causes.
Iron. A healthy diet with plenty of iron rich foods (red meats, etc.).