During today's server mess, I tried to reinstall the app on my iPhone 6s. Then, when rebooting it, it had problems with the Google password and I had to reset it through Google. Now it forced me to start a new Pokémon Go character. How do I find all of my "hard earned" data?
If you haven't signed in yet then you can sign in with Google again and your "Hard Earned" data should be restored
If you have tried signing in then the short answer is: you don't
All pokemon go game data is stored on a server, if you have logged into your account and your data isn't there, there are two possible problems
1) The servers aren't working properly (You have to wait for it to start working)
2) your data was cleared(most likely as instead of losing data most people just couldn't log in)