What Is The Best Treatment For My Teenage Vegetarian Son With Iron Deficiency, And Is IV Iron Therapy Advisable?

Sir Namskarm, My son 17 years old and have iron deficiency. Hb is 7.9. , He is vegetarian. Please give me some advice and medicine, supplement for the said reason. Also my doctor told me to treat with IV. Is it a good or not? Thank you, waiting for your valuable advice.