You will need to go to the Surrogate's Court.
I am a former federal and State prosecutor and have been handling criminal defense and personal injury cases for over 17 years. The above answer, and any follow up comments or emails, is for informational purposes only and not meant as legal advice.
If all you need is updated letters testamentary, that is something that can be done quicker than it will take for you to read this response. If, on the other hand, the estate has been closed, there may be more steps involved. It's hard to answer you definitively, because you don't indicate whether the problem is that letters testamentary are more than six months old and thus just need to be update. You also don't indicate whether the newly-found assets are significant enough to markedly increase the value of the estate, thus requiring at the very least that a higher filing fee be paid, or whether the assets held by the Comptroller are modest in value. Most (but certainly not all) assets held by Comptroller as abandoned property are quite low in value. If you have any difficulty with this, you should consult with an attorney. You can feel free to contact any of us here on avvo.
Good luck to you.
Michael S. Haber is a New York attorney. As such, his responses to posted inquiries, such as the one above, are limited to his understanding of law in the jurisdiction in which he practices and not to any other jurisdiction. In addition, no response to any posted inquiry should be deemed to constitute legal advice, nor to constitute the existence of an attorney/client or other contractual or fiduciary relationship, inasmuch as rendering legal advice involves the ability of the attorney to ask appropriate questions of the person seeking such advice and to thus gather appropriate information. In addition, an attorney/client relationship is formed only by specific agreement. The purpose of this answer is to provide the questioner with general information, not to outline specific legal rights and remedies.