I did the hero bracer quest a couple days ago, it was very simple.

Once you have the shackles, go under the arena in south qeynos and talk
to Rothkar. Say "what about the second escaped gladiator?" for him to
talk about the mino hero. If your faction is bad he'll say you haven't
proven yourself. If so, play the lvl 11 faction song on him and problem
solved. Give him the shackles and you get the bracer placed in your
inventory.