Download the whole package for Kayra including the freeCAD files (for modification), STL files (printable files for your printer), gcode files (“rendered” files for Prusa MK3S to be printed in PETG) and certainly the whole software (for the host computer as well as the controller(s)).
Click on the green “Code” download button:
Click “Download ZIP”
The resulting ZIP file will contain a folder called “STL” as can also be seen on the github page.
The STL files are the relevant files for simply printing and building Kayra when you bought the suggested servos.
Go on to software setup.