By external software after taking photos. Nano doesn't do it alone, it only takes photos. Assembly must be done by third-party software or application.
You will need many photos then process them with OpenDroneMap or something like Meshmellow, etc..
Autel is not giving us mission planning because they think that the only people what want to do mapping or photogrammetry are industrial contractors with bigger drones.
So for now you will have to capture all the photos, with appropriate overlap, manually.