How do you mention your narrator is an unreliable narrator in your query? The current book I'm querying has such a narrator but it isn't revealed until the very end so I don't mention it in the query. I'm wondering if this is better mentioned in the synopsis (it is) or if this is something that needs to be addressed in the query right from the beginning.
While I am indeed the source of all wisdom in publishing (ow! LIGHTNING just hit me!) one good way to find the answer to questions like this is to see how other books with similar devices/plot twists are handled.
That means you have to know what books have unreliable narrators which is a good thing since those are your comp titles.
And that leads you to the answer to your question:
You do not EVER tell anyone in the query that it's an unreliable narrator. That's akin to giving away all the plot.
You can however use books with unreliable narrators as your comp titles, and a discerning agent will think "aha! a clue!"
As for how unreliable narrators are covered in the query, here's Who Killed Roger Ackroyd? by Agatha Christie:
Roger Ackroyd knew too much. He knew that the woman he loved had poisoned her brutal first husband. He suspected also that someone had been blackmailing her. Then, tragically, came the news that she had taken her own life with a drug overdose.But the evening post brought Roger one last fatal scrap of information. Unfortunately before he could finish reading the letter, he was stabbed to death.Who killed Roger Ackroyd?
The query doesn't start with the hero (Hercule Poirot, the detective) or what he wants or what's at stake. It sets up the premise of the mystery.
Check out other examples, and find ones that are closer to your book than this one is. Use that as a template.