As a child your breast tissues and glands were not developed. During puberty your breast tissues started to develop. Your breast tissues stopped developing before they reached the size that you desire.
Recreate the situation and circumstances just before your breasts stopped developing. Now stimulate the hormones in your body to develop the breast tissue.
Visualize yourself how you want your breasts to look in your clothes.
Now increase the blood flow to your bust area, stimulating your breast tissue to develop into the size of bust you desire, appearing the way you want to look in your clothes.
Now visualize the pectoral muscles and the muscles around your breast area developing to hold your bust firmly to prevent sagging.