Before plugging the dongle in the new server, you will need to install the dongle drivers.  The latest dongle driver installer can be downloaded here:
http://downloads.12dmodel.com/v11/11.1.11/11.1.11.7/12d_dongles_installation_13_Oct_16.exe

When installing, you will be asked what type of dongle is in use. The dongle type is easily recognised by the colour:
* Green – Wibu
* Silver – CodeMeter

After installing the dongle drivers, plug in the dongle.

On the client computers, you will need to update the env.4d or env_configs.4d so that it is pointing to the new server location.  Again this will depend on the dongle type.
Instructions can be found in the Network Dongle Manuals.
Wibu http://12dmodel.com/downloads/Documentation/V11//12d_Installing_Network_Wibu_24_Jul_15.pdf
CodeMeter http://12dmodel.com/downloads/Documentation/V11/12d_Installing_Network_CodeMeters_18_Sep_15.pdf