Is it possible to log back into a Pokemon Go account?

So I had 20+ Pokemon on my account and today when I tapped on the app, it brought me back to the original screen when you first start playing. My friend who signed up tested using my username when she first started and my username was unavailable, meaning the account still exists. I don't have the password for the account, but I do have the email. So I wanted to know if it was possible to log back into an account?

Yeah. do a password recovery (password reset).

If it's tied to the email you say it's tied to, then it will send the reset instructions back to it.

But, it may make you do it on the WEBSITE and not the Pokemon GO app itself.

I haven't used PkGO for a while.