The account number is the email address you used when you first registered.
Do you still remember it?

(You can look for your usual email address.)
If you have retrieved your account but don't remember your password, you can enter your account in the login interface of the app, click Forgot Password, and then reset your password.
If you really don't remember the account, you can register a new account with a new email, and then reset the camera and rebind the camera.