A decision by a judge is automatically appealable when it is a final order. A final order means it makes a final disposition of the case. This is not automatically appealable because it sounds like the judge dismissed the motion to amend and did not dismiss the entire case, correct?
If it is a final decision, (I am incorrect in the last sentence) then you can appeal the issue by using Federal Rules of Appellate Procedure Rule 15. Using that rule you will have to flle a petition for the court to review the administrative agency's decision. You must file for the appeal within 30 days of the judge's decision.
If it is not the final order by the judge (I am correct in the first paragraph) then you will need to wait for a final order before you can challenge the motion. there are some motions that can be appealed through a process called interlocutory appeal. To use that process use Federal Rules of Appeallate Procedure Rule 5. Rule 5 requires a different type of petition, a petition for permission to appeal. You have to file this, generally, within 30 days of the judge's decision.
I recommend you hire an appeals attorney. Appeals are time consuming and complicated. Deadlines and time lines are very strict, and appeals are often difficult to win because of the standard of review. If you'd like to discuss this further, feel free to contact me, my information is on my avvo page of on my website. You can also find more broad information about appeals on my blog.
Best of Luck,
Shannon K. McDonald