Can malnourished person be back to the normal human curve and how?

Yes, often.: Children are resilient. "Catch-up growth" can occur when proper diet and control on illnesses is achieved in many cases. Certainly, prolonged malnutrition may have long term effects but may be minor if good nutrition is restored and continued in time. Effects on children before age 2 are more concerning, in terms before full brain development. No one knows how much.