28, 5'9, BBL 5 years ago, how to resolve sagging buttocks? (Photo)

Thank you for your picture and your question.

Toning your muscles and achieving symmetry can be achieved with surgery and exercise. You will benefit from another BBL to make your buttocks more symmetrical, or liposuction of the bigger buttock depending on what's your goal. But after surgery, when you're fully recovered, you should exercise as much as you can. Exercise is what will help you strengthen your muscles.

To make an assessment regarding the outcome of a plastic surgery procedure we generally need to see a complete set of proper before and after pictures. If you don’t have your before and after pictures, then contact your surgeon and ask them to forward the pictures they took.
Most people have some asymmetry of their body as baseline. We need to know how much of this asymmetry was present before surgery and see what you look like before to have an idea of what was done during the procedure.Some plastic surgeons are in the habit of removing fat from the upper thigh, in order to make the buttocks look bigger. This creates an unnatural transition from the buttocks and hips to the thigh, creating a saggy bottom, or a bottom. That sometimes looks like a popsicle.
Delivering consistent quality, liposuction and fat transfer results is more difficult than most people realize. The number of plastic surgeons who truly mastered these procedures are the small minority. They are a significant number of plastic surgeons who are not particularly good at either Liposuction or fat transfer.
Revision work, or secondary body, contouring procedures are generally more difficult, and more complex with greater uncertainty than primary procedures.
Anytime somebody wants to have a revision work they should be extremely selective in their choice of providers. I suggest doing that I having multiple in person consultations. Best,
Mats Hagstrom, MD