need to unregistered betheme on old website already dowen

how to remove the license from an old website theme

You need to talk to the author but bear in mind that if the theme has been used on a project already, not all authors allow the license to be re-purposed and may require a new license.

i already need to remove the license from the old one and use it in a new website let me contact auther

The author is the right person to deregister it but not all authors allow end product use to be swapped once already used previously regardless of of the original site is no longer active