82% after ~500 cycles is fairly normal (I'm at about 75% after 680 cycles). Replacement is possible either DIY or via Apple.
In general degradation rate increases at high battery temperatures (e.g. >35deg C)
There is nothing that can be done: it's physical degradation of the battery structure. And it's complex:
"
five principal degradation mechanisms that are most commonly considered to be the cause of battery degradation during normal operation. These are SEI layer growth, lithium plating, PE decomposition and particle fracture at both electrodes. These five principal degradation mechanisms interact with each other and give rise to thirteen secondary degradation mechanisms"
https://pubs.rsc.org/en/content/articlelanding/2021/cp/d1cp00359c#