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.

Unfortunately effective significant correction of breast asymmetry shown in your photograph requires a lift on the lower side breast.For more information on correction of breast asymmetry please read the following link:

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