Button Icons

[JadeForlorn]

I apologize as I'm sure this has been answered but my search-fu is weak and I couldn't find it.

I am attempting to modify a group window mod I downloaded to make it more friendly for my inquisitor. I am hindered because I do not know where to find the names for the icons for certain abilities. For example:

I do not have Call of the Hero so I am trying to change this:
<Button BackgroundOpacity="0.000" LocalTooltip="Call of the Hero" Location="3,24" Name="ZCotH" OnPress="useability Call of the Hero target_previous" ScrollExtent="23,23" Size="23,23" Style="/ButtonStyles.invisible" />

to cast Favor of the Repentant, but would like to make the icon match that which is the spell.

<Button BackgroundOpacity="0.000" LocalTooltip="Favor of the Repentant" Location="3,24" Name="ZCotH" OnPress="useability Favor of the Repentant target_previous" ScrollExtent="23,23" Size="23,23" Style="/ButtonStyles.invisible" />

Is what I have so far, which I believe will work just fine even with the incorrect icon. Am I correct? Even so, if I am correct the inproper icon just doesn't work for me... I assume the icon name in this string is ZCotH, so how do I find the icon names for my other spells?