Can't exchange dim tree for fallen amour.

Hello, I need help I been trying to exchange my dim tree for fallen amour, I have tried everything and am not sure what I'm doing wrong, here is some print screens of my dim tree c 10 and flame of despair.

 

you need the knowledge of the quest "the three legendary blacksmiths" , on average, that quest is given to you by the dark spirit , chek that first

 

As @reaXtime pointed out, you need the knowledge called "The Three Legendary Blacksmiths of Mediah", which can only be obtained by completing a quest series in Mediah (Level 51+).
This quest chain starts at The Three Blacksmiths, given by Tulem, the <Arms Dealer> of Altinova.
Check if that's the case and let us know.