Hire a lawyer. A modification may be possible, depending on timing and the whole story.
This answer DOES NOT establish an attorney-client relationship. This answer is based on the limited information provided and is not intended to be conclusive advice. There are likely other factors that might influence or change the advice after a more lengthy consultation.
You need a lawyer ASAP. If a decree has been signed, you are under tight deadlines to try and undo what the decree orders. If at all possible, you want to file a motion for new trial or notice of appeal within 30 days of the date the decree was signed. There may still be some options available after 30 days have passed, but they are much more limited.
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