Unlock Materia Tiers up?

I was return 2 month ago from close year ago.
Noticed we had NPCs as Materia melder!

But, My character had skill Materia Tiers II.

Want get unlock III. But, I can't?
I knew, learn from The Bonfire. But, NPC don't give me unlock III as I'm 50lvl crafting

How?

Sorry bad english.

Boop.
Sorry. I need know

There is no third level of materia melding. The original tier lets you attach materia to guaranteed slots, and the second allows you to attach materia beyond those guaranteed slots with a low chance of success, up to a maximum of 5.