How can i lower my rbc naturally?

Bleeding: Bleeding is the best way to lower RBC. But it depends on what you mean by naturally. In all seriousness, if you need to decrease your RBC, the best way is phlebotomy at your doctor's office. If you smoke, stop. If you have sleep apnea, use CPAP. Make sure your doctor has excluded "Polycythemia Vera" which is like a precancer of red-blood cells in which you have too many and need medication.