The same way filebot and any other tool does - the file needs to have some label, either an absolute episode number or a season + episode number. I’m not aware of any tool that is able to look at the contents of the video to figure out which episode it is visually without any information from the filename - but I’d be happy to be proven wrong because I would be impressed.
Sonarr/radarr does analyze the content somewhat but that’s just for gathering resolution, codec, HDR, audio languages, and subtitle information, which can all be added to the filename format for inclusion during renaming.