How do I regain ownership of a domain name?

A 501c(3) organization changes its name. Part of the name change is to change internet domain name. Although not in writing anywhere, the intent of the organization is to own the domain name through a registrar. However, the volunteer making the changes for the organization, instead of creating a registrar account in the name of the organization, registers the domain under his own personal registrar account and now says he owns the domain name. This leaves the organization at risk as the volunteer could, at any time and for any reason, change the domain name servers at the registrar, thereby making the website and email inoperable. In Texas, what recourse is available to cause him to reassign the domain name to a registrar account held by the organization?