Print the STL exactly as it appears, vertically. Add 10 mm brim for better stability during print.

Remove the legs holder tissue from holder tubes, using the printed reinforcement as a template and mark the holes on legs holder tubes using a permanent marker (upper side only)

Drill the holes on marked dot with a 4 mm drill bit (it's designed for use with M3 screws)

Check the holes by mounting the reinforcements, the screws and the nuts

Remove the reinforcements, the screws and the nuts and put the legs holder tissue on holder tubes

Place the reinforcements on the legs holder tissue and make the holes on it (using a scissor or a screwdriver). Cut four pieces of thick tissue (i have used jeans tissue) and make the holes on it. Mount the reinforcements with the thick tissue, the screws and the nuts

Cut the excess of the screws, pay attention to remove all the burr with a file or sandpaper. I've assembled all with M3X20 screws with allen rounded head.