Dents in the superficial dermis may not need to be undermined and injected, but may also not respond to the fat injection. Best to wait and see as the swelling subsides.
After liposuction and Braziliian Buttlift, it typically takes approximately 6 weeks for the swelling to resolve and for you to know what your final results will be. That being said, it is unlikely that the dent that you show in the photo will "fill in" or get any better. Ask your surgeon if he/she saved any fat (frozen) for a touch up, if not, you may need a secondary touch up procedure to smooth that area. Good luck!