You can simply remove your license key on your current computer. In order to do so, in the on the Viewer ribbon toolbar navigate to the Help tab and select License Key Storage.... In the opened window select the preferred key and click Remove selected key. Then proceed with adding the license key on your other Viewer as described in this registration guide. Please note that despite its name, the Endpoint license key is added on the Viewer's side as well.
Alternatively, you can simply add the license key to your new Viewer and use it there as you are not restricted to a specific workstation with any license key, especially with an Endpoint license that only limits the number of the remote Hosts. Fore more information please see this License Comparison table.