Thank you for the question. You may wish to post photographs with your next question for more specific responses.
Often, improved breast symmetry can be achieved with breast augmentation surgery. Careful breast implant “pocket” dissection, and the use of different size/profile of breast implants may be helpful in doing so. Sometimes, depending on the patient's anatomic starting point, breast lifting/reduction surgery may also be helpful.
Keep in mind, that realistic expectations are important; I ask patients to expect the breasts to be “sisters, not twins”, despite best efforts.
My best suggestion: select your plastic surgeon very carefully. Ask to see lots of examples of his/her work achieving the types of outcome you will be pleased with. Then, communicate your goals very carefully as well. In my practice, I find the use of goal photographs, in bra sizers, and computer imaging very helpful during this communication process.
You may find the attached link, dedicated to breast asymmetry concerns, helpful to you as you learn more. Best wishes for an outcome that you will be very pleased with.