From the Patch Panel, select "Export MVR" to launch the MVR export Dialog.
You will need to provide your own GDTF files which will be included in the MVR file for your fixture types. Once you have pleased them in a directory, choose that directory in Step 1.
The dialog will then scan that directory and provide a "best guess" for which GDTF to use for each fixture type detected in your scene. You may override this guess and choose one that works better for you.
You may be presented with an error in the export statistics such as the following image: 
To correct the error, you will need to fix any duplicate fixture IDs or patches, as these will not be compliant with the file specification. Once you've corrected the errors you can export the MVR file for use in other applications.