In order to modify any provision of your Judgment for Dissolution or your QDRO, a court Order must be entered after proper notice and motion. Return to your former attorney or hire new counsel and get this matter taken care of. If this is all done by agreement, it should be quick and not very costly.
If she was awarded part of your pension plan in the divorce, then court action will be required for her to give that back to you. Technically, the court does not have jurisdiction to modify the property award. If can do so if both of you go and ask the court to do so (its called revestment). If there was a QDRO entered, you will have to do a new QDRO terminating the previous QDRO.
You do not indicate if your case has even been filed. If it has not, talk to an attorney about a post nuptial agreement. If it has been filed and is still pending, be sure her waiver is spelled out in your judgment. See a lawyer in any event.