We want to start by prefacing this article with the fact that, while it's technically possible to reroll in the new KOF: Survival City, we can't actually recommend it, simply because it takes a long time to do so every run. This slowness is mainly due to the fact that the gacha system is locked behind story progression, and you can only access it upon reaching chapter 4 in the main quests.
Rerolling in this game is quite simple and straightforward, in theory. Nevertheless, the main caveat is that it can take a while since you'll need to progress relatively far into the story in order to access the gacha feature. Barring that, if you're committed enough, it's technically possible to reroll and recruit some of the best fighters from early on—if you're lucky enough, that is.
Each cycle should take you around 30 to 45 minutes, depending on how focused and quick you are. Also, keep in mind that if you're playing on BlueStacks, you can easily double, triple, or even quadruple the number of pulls you can perform per cycle, by playing on multiple accounts simultaneously.