If you don't understand how to file an amendment, I would contact a lawyer who does family law in your jurisdiction. If you're only asking for them to draft an amendment that you would then file yourself, the lawyer will likely quote you a low reasonable flat fee for the amendment.
Disclaimer: This post does not create an attorney-client relationship. This post is for informational purposes only and is not intended as legal advice. This post is not a substitute for holding an in-person initial consult with an attorney.