However, there must be a considerable degree of recovery. One month after quitting smoking, the cilia in the lungs can regenerate, thus starting to remove tar and dead cells from the trachea. This is why many people start to spit black phlegm after quitting smoking.
The human body has its own recovery function. The best way to protect the lungs is not to smoke, stay away from polluted environment and do more exercise. Maintain a good lifestyle.
Of course, it is unlikely that you will completely return to the state where you have never smoked at all.