How can i use Fiery Sword Hilt on pvp char ?

I just have noticed that I don't have Fiery Sword Hilt unlocked. It really suprised me cause i had few Fiery Dragon Swords. So i picked one and salvaged it. Got a Fiery Sword Hilt in my invectory but still it is blocked when i try to start pvp character. Well i tried to add this to other sword but nothing changed. Last thing i tried is to add this to unidentified item to then do identification and unlock fire dmg. But it write me that I cannot add this before I do identification. I really don't have idea how to unlock this. Problem is that this sword is identified already when it drop. So how to unlock ? Strange thing is that i have unlocked earth dmg but I don't remember when and how i did it.

So question here is, how can I unlock fire dmg ?

Identifying a weapon with Fiery as a prefix other than Dragon Swords.

i have no idea but i would like to buy said sword
if you r selling pm me