If you had an account on the old phpBB forum, reset your password so you can log in. Discourse has different rules for allowed passwords, so you might need to choose a different password than what you used for phpBB.
If you no longer have access to the email address you used to register on the old phpBB forum or can’t reset your password here for any other reason, email me at be@mixxx.org or send me a private message on the old phpBB forum.