Can I log back into my Pokémon Go account if I'm told it doesn't exist? [duplicate]
Solution 1:
When you create an account you either have to have a password for your pokemon trainer account, or log in through your google account, which would mean your google username and password. This means you can't start without having a password.
If these options aren't enough, you can probably find a relevant topic or email address to contact Pokemon Go support on their website. https://support.pokemongo.nianticlabs.com/hc/en-us
*on a side note. As long as you can provide Niantic with the info registered to the account they should be able to recover it (i.e. email adress, original user name, etc). But yeah, if you are registered with Google it shouldn't be having problems.
Solution 2:
Just to clarify, if you've already got an account and it asks you to sign up again, just sign up with the same account and you'll still have all your progress.
You can also log into a different device with the same account.