Building muscle underneath sagging breasts

Has anyone done this? Did it help? I’m currently losing weight and they’re getting saggier by the day.. I’m 18 and just want breasts like every other girl my age.

Edit: I know how breasts work and that you cannot change the actual shape or tissue. That’s not what I’m talking about. I’m talking about the muscle underneath helping them a bit and I wanted to know what others experiences are with it.