How to migrate a site in other domain maintaining the active license?
For migration if yoiu don’t know how to do this then will be better to hire a freelancer. You can hire freelancer from WordPress experts at Envato Studio. About active license you have to deregister the license from old domian first then have to register the license for new domain. So, please contact Theme Author or check their online support forum hope you will get help there.
For migration there are lot of services where they migrate your site for absolutely free when you purchase hosting from there, Name cheap is doing this service.