Print the STL exactly as it appears, vertically. Add 10 mm brim for better stability during print.
2
Mark the holes
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)
3
Drill the holes
Drill the holes on marked dot with a 4 mm drill bit (it's designed for use with M3 screws)