In iOs there is no need to clear data, just uninstall and install again.

if you were asking about the best heroes you should try to get when reroll: Velvet, Leon, Cress and Estelle are the best choices, and and a reroll will be successful if you get one of them and at least another SSR

I didn't write, but in the page where i write walkthroughs there is a reroll quick guide: https://www.mejoress.com/en/tales-of-crestoria-reroll-guide/. And at the end of the guide there is also a link to the complete Tier List.