1984 C20 straight 6 Tranny refill

[AbsoLucy]

..need to refill tranny fluid on my recently purchased 1984 C20 Pick up. Where do I pour the fluid? Do I pour it into the dipstick line ??? I can't find anything that says 'transmission" and want to avoid pouring it into a completely wrong location like an idiot

[GoToGuy]

A little more info helps. Manual or auto? And yes its the one near the firewall. Not the one in engine. And get a service manual don't guess. Guessing is always expensive.