Thanks for your query.
First of all its good that you have left smoking
and that should actually relieve your anxiety
about getting sick . Anyways the damage done to lungs cannot be reverted back but further damage can be controlled by following a healthy lifestyle , regular aerobic exercise
30 mins daily for at least 5 days a week , doing yoga
exercises aimed at increasing the lung capacities , taking a nutritious diet and avoiding any kind of addictions.
Further any symptoms like cough
, loss of weight , blood in sputum , breathlessness , repeated lung infections etc should be watched and promptly investigated by a specialist.
Take care .