You can take a look at the config to see who it is set to use it on (it's in the class_config folder), and you have the ability to copy the config to customize it (on your class tab).
A little bit of Lua knowledge helps but isn't strictly required, would be happy to help you out in discord, we have a channel for mercs!
Edit: it should be buffing on the bard, not sure why it wouldn't be, unless it's general stuff, something like that it wouldn't stack, it's blocked, etc.
Could help you access the debugging to see what's going on if you are interested