>>50741205he doesn't, again they are legendary pokemon and don't evolve
You unlock the forms as the story progresses.
I never used Trishout X because mine had 31 attack iv's so I just leaned into it. kept using Trishout T until I unlocked it's final form
Trishout has some very powerful special attacks available and his X form can make much better use for them.
Even though my Trishout was poorly suited for it, I used his X form for a few boss encounters just to abuse Boomburst. every pokecenter has a free move relearner
