@luthis

Go back to the tracker you got the file from and re-download the torrent. Make sure your client is pointing to the correct location where the file is stored. [set location, verify local data] and it should just seed it.

Try this tool to match a torrent file to its data: https://github.com/JohnDoee/autotorrent

Yes if you download the torrent files

Depending on which client and how long ago you deleted the torrent, you may still have a copy of it in your temp files.

You can create a new torrent for that data if you want, that way you can continue seeding it in a new torrent swarm.

Otherwise if you intend to seed in the old torrent swarm then you need the old .torrent for that. Search around maybe you'll find it (or if you remember where you downloaded it originally that's even easier).

Do you mean deleted the torrent entry from client or the data files?

If just the entry you can add the torrent and set it to discover the existing data directory. Steps might vary by client.

If you meant seed deleted data, AFAIK its not possible to seed data that you dont have. No idea why you expect that to be possible.

Depending on your client, there may be different directories for complete and incomplete torrents, so you may have to put the downloaded files in the incomplete folder. If your client only checks the incomplete folder when starting a torrent.