The point of re-rolling is so you can get one of the stronger characters through the games very first character summon it gives you.
The main way to Re-roll is to uninstall the game if you don’t get the heroes you want. Then reinstall it and you’ll be at a fresh start and can re-roll your account for better characters.
Depending on your device it’ll be different on how long it takes. Emulators like Nox are best for Re-Rolling but you can still do this easily on Android or iOs.
Once you get passed all of the tutorial stuff, you’ll be given a free 200 gems to use for a summon. This is where you use your summon to try and go for one of the better heroes.SSR heroes are the best, while SR come in secondary.
Before summoning, however, you want to look into the banners going on and see which hero you want to aim for. You could just spin wildly and keep Re-Rolling until you get any strong ranked hero.
Or you can focus on one hero and keep Re-Rolling until you end up getting that one. It’s best to pick what kind of hero you want, that way you’ll be satisfied with your Re-Rolling efforts when you get them.
There a quite a variety of viable heroes. Ruby, Cain, Rue, or any of the White or Dark Knights are very good.