Crash Data Recorders (for all cars) are not designed to be "cleared". Once written, the data stays in them. Another used module will contain someone else's data. In some cases a FLASH memory programmer can be used rewrite the entire Flash chip. However, in order for it to function, it must be written with an image of the original, virgin data mask, and those may change with production changes. Thus once there has been an impact, you should replace the entire module with an OEM replacement part. There are services that claim to clear and rewrite them, but there's no certainty its been done correctly.