Open Utilities > Plugin Manager and select export3DM to enable the plugin. The plugin will be listed under Autodesk App Store. Please select export3DM_2017 ( Alias 2017 or Alias 2016) or export3DM_2018 for Alias 2018 or export3DM_2021_3 for Alias 2021.3
Select the Auto Load option to automatically load the plugin the next time Alias starts.
The plugin will be installed under File > Export menu, as Export 3DM

Click on Export 3DM either to save the contents of the current stage or active objects to a 3dm file.
Open Export 3DM Option box, to select either All objects or Active objects.
The following datasets are translated

The installer that ran when you downloaded this app/plug-in from Autodesk App Store will start installing the app/plug-in. OR, simply double-click the downloaded installer to install the app/plugin.

You can unload the plugin without uninstalling it by unchecking the "Load/Unload" check box associated with the plugin in the Autodesk® Alias® Plug-in Manager. You may have to restart Alias to completely unload the application.

Please ensure the following pre-requisites are met. 
.NET framework 4.6.1 or above. Download the framework from https://www.microsoft.com/en-us/download/details.aspx?id=49981 
Microsoft Visual C++ 2019 Redistributable or above. Download the files from https://aka.ms/vs/16/release/vc_redist.x64.exe

To uninstall this plug-in, exit the Autodesk product if you are currently running it, simply rerun the installer, and select the "Uninstall" button. OR, you can uninstall it from 'Control Panel/Programs and Features' (Windows 7/8.1/10), just as you would uninstall any other application from your system.

Limitation: The default layer in Alias is called DefaultLayer and cannot be deleted or renamed.

• Work Around: The translator will rename the layer to "_Default_" so that round trip transfers don't end up with multiple layers called "DefaultLayer".

Limitation: Some trimmed periodic/closed surfaces may not get trimmed properly.

• Work Around: Please detach such surfaces into two before the transfer or convert them to shells, using SurfaceEdit->Stitch function.

Limitation: Some complex multi-level instances might not transfer properly.

• Work Around: Please use Edit->Expand Instances to create real geometry before the transfer