I am not sure the exact extruder used on the Robo R1+, but almost all extruders come with different nozzle size options. You would just have to Google nozzles for the extruder being used on your machine. It would need to be the nozzle meant for your extruder.
You could of course also upgrade the extruder to an E3D like I use in the video, and then you can use the exact nozzles I use. You would just need to print a new carriage and buy the parts.