To activate a server license, use the LicenseActivator.exe software. That software is bundled with The Report Viewer.
LicenseActivator.exe is installed next to the The Report Viewer executable. Look at C:\Program Files (x86)\Report Viewer Limited\The Report Viewer\LicenseActivator.exe or a similar location. That software will allow you to activate The Report Viewer.
Server licenses are attached to the specific computer. You can use the LicenseActivator.exe to reactivate your server licenses on the same server.