If you are receiving an error with the message "A user already exists with the credentials you've provided..." it may be because that the email you are using to register already has an account associated with it.
I recommend using the steps listed in the knowledge base article to reset your password. The link to the article can be found here.
If you continue to face difficulty, you can reach out to the Unified Talent Applicant Support team. The team should be able to gather information on your account and help look into options to recover or remove your existing account. You can follow this direct link to contact the Unified Talent Applicant Support team.