If you absolutely cannot find a working driver for your exact model, your final resort is to restore the laptop using Sony’s original (ISO images can be found on archive.org). Those discs contain the complete, factory driver set—including the working Assist Button.
If the drivers are installed but the button still doesn't function, try these methods: sony vaio assist button driver download link
After installation, restart your laptop. The Assist button should now launch VAIO Care. If you absolutely cannot find a working driver
The core driver that makes the button recognized by Windows. The software launched by the button for diagnostics. Sony Shared Library Communicates between applications and the firmware. The Assist button should now launch VAIO Care
After installing, reboot. Then press the Assist button while the PC is off – it should power on into VAIO Care Rescue. If it only works in Windows, reinstall VAIO Care (available on same archive links).
If you install the wrong driver: