I'm amazed to see, I can't login into my account from anywhere other than the app since they are not accepting my email, Saying - " No account with this email ". Now I want to change my name but unable to do so. Please help.
The email and password fields are for Stack Exchange login only. (Used to be OpenID, now it's just a plain email/password login.)
You most likely used Google or Facebook to create your account (and maybe forgot you did that), so you need to click either the Google button or Facebook button:
This will redirect you to the proper place where you can login to the provider, then you'll be redirected back to where you came from.