I'm not too familiar with "unl", but VIRL configurations are stored in a single XML file. The file has an extension of .virl that VM Maestro can open. I would suggest recreating the topology using the builtin VM Maestro tools.
For tutorials, please visit: VIRL Getting Started Tutorial
I'd also like to suggest reviewing VM Maestro's Help Documentation. To access this resource, simply open VM Maestro and navigate to Help > Help Contents
Cisco Learning Network