Download the STL files from here
Using your 3D Printers slicer, load and prepare the files for your 3D printer
Although I used a grey PLA, it should print using most common types of filament.
It might be worth considering printing the button assembly in a different colour filament.
To assemble the case put the buttons through the button holes from the inside.
Fit your Nano Probe electronics into the case, probe first into the round hole, ensuring that the two LEDs push through the holes in the front. Gently push the PCB into place being careful not to put any pressure on the screen.
You may find that the button holes and LED holes need some cleaning up to fit nicely, depending on your printer, filament and settings.
Once in place solder the power cables though the rectangular hole at the other end and solder to the PCB (making sure they are the right way around!)
Before powering up your Nano Probe, have a quick read of Using your Nano Probe
If everything works OK, Clip on the cover, you can glue the cover on with any glue that works with your choice of filament. (probably a couple of drops of super glue)