You have to go to TMDB's website, or TVDB, and look at what "episode number" they use for each special you have. There is no mechanism in Jellyfin to help you with this process. YOU tell it what you have and it gets the metadata.
Jellyfin 10.10.1 (Docker)
Ubuntu 24.04 LTS
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
3x WD Red Pro 6TB CMR in RAIDZ1 (JF Library)