Sign in with the email address and password you set when the account was created.
Forgot the password? The sign-in page has a reset link: enter your email and, if an account exists for it, a message with a reset link arrives. The link opens a page where you set a new password.
Account → Security lists your active sessions - every device currently signed in, with its IP address and last activity. If you see one you do not recognise, press Revoke next to it and change your password straight away.
If two-factor authentication is on, signing in asks for a six-digit code after the password. Lost access to your authenticator app? Open a ticket from the email address on the account so we can verify it is you.