Not really sure if the will can help you in this case, since based on this article https://www.expatden.com/thailand/last-will-and-testament/#Shares_in_a_Thai_Company, it's upto the director's board to do it. And it's usally done by the minutes of meeting and change the shareholder name with the Department of Business Development.
However, for this kind of legal staff, it's best to talk with a lawyer directly to get a precise answer.