Install either e.g. Arduino Lab for MicroPython or Thonny to access via REPL/Files the internal file system of the CyberBrick Core.
The original code of CyberBrick MicroPython files is under: GitHub - CyberBrick-Official/CyberBrick_Controller_Core (under src/app_rc subfolder).
The file to modify would be the src/app_rc/bbl/servos.py at line 77.