Problem with Icon Herioc Will or lack off it

[XDNAngel]

Hoping somebody can help me here. I used the raid finder to tank the Fall of Deathwing raid. The second part to the Dragon Soul raid. On the boss Ultraxion the tank aquires the buff called Herioc Will. The tank needs to use this buff to move in and out of twilight to avoid damage from the boss. Problem was I could not find the buff anywhere on the Nui screen to use or click on. Could somebody point me in the right direction on the Nui dashboard as to where the button is to use the buff .