The Arizona statute that pertains to your question is: Revocation of Claim to Paternity Rev. Stat. § 25-812. You can read more about it by searching for my legal guide on paternity here on Avvo, but I recommend you contact a local attorney to help you as soon as possible. There are many in your area with profiles here on Avvo, I recommend you contact at least two before deciding how to proceed. Good luck!
Generally, you must make the correct claim in any action with the court as soon as possible. Do not delay if a devorce is pending. If you fail to raise the issue, you may be deemed to have waived it and the ex will be conclusively determined to have been the father.
In addtion to the understandings and conditions set forth in the Avvo website, it should be recognized that no attorney client relationship is established by answering general questions on the site. Seek your own personal legal advice on each and every issue.