I’m no expert, but I am guessing the authorities in the country of whoever owned the satellite would be notified and either it would be dealt with quietly or we would all go into panic! I am not sure if a satellite would be able to sense a form of life though – Camilla will know!
I supposed it depends on what kind of life form it is. We’ve sent robots and satellites to other planets and to comets and they can have scientific instruments on them which they can use to detect microbiological life. If it was a highly advanced alien then we could maybe intercept its communications with one of our satellites’ anetennas. I think we’d then inform the science community and maybe the government.