One of my breasts is sagging but not the other. Is there anything I can do to make it symmetrical without surgery? (photos)

Unfortunately,
exercises won’t help, since the problem lies in the increased looseness of
supportive tissues rather than an underdeveloped muscle, so surgery is your
best bet. Although no woman’s breasts are perfectly symmetrical, the degree of
asymmetry you’re concerned about really can’t be resolved except through
surgery. Usually, the options come down to a reduction and lift on the larger
breast, or a modest-sized implant in the smaller breast. Sometimes, a
combination of both approaches works best, perhaps along with using small
implants in both breasts to add volume and firmness. In general, if the perky,
uplifted look is closer to your ideal, then the lift/reduction (with or without
implants) is probably going to give you the best results.

Thanks for your picture. You can very easily gain symmetry to your breast by having a breast lift. Think that a lollipop lift will probably work very well for you. You obviously need more lift on the right than the left but I think both both breast  need to be lifted to some degree. Seek several board-certified plastic surgeons. Good luck

Based on your photos, your breast asymmetry is fairly significant. The larger and more droopy breast would need a lift and reduction, and you may very well need surgery on the breast you like in order to give the best chance of symmetry overall. Clearly, you would benefit from talking to a board-certified plastic surgeon about these issues. Breast development is usually complete by age 22, so they probably will not change significantly. No exercises will help, unfortunately.