You can easily convert a standalone licensed Civil 3D 2016 to network licensing by making a simple registry edit.
- Shut down Civil 3D 2016.
- Open the Registry Editor.
- Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Autodesk\AutoCAD\R20.1\ACAD-F000\AdLM
- Change the Type value from 2 to 1.
- Restart Civil 3D 2016.
If your machine is already configured to find the appropriate network license from your license manager, you shouldn’t have to do anything else, it will start up just fine.
Otherwise, you’ll need to set a Windows Environment variable as shown on this page so that Civil 3D can find the license it needs.