You'll get it shortly after solving the five bells puzzle, going through the door and up a ladder.
It leads you to a mysterious room in the underground section, where there are two swinging pyres that you can set alight.
Resident Evil Village Treasure Map Solution & Location
It's actually somewhere you'll have been before as part of the story, but the map leads to a locked door in the dungeon.
You'll first need the Iron Insignia Key from the Opera Hall piano, having completed the piano notes puzzle, and then you can head back to the door to unlock it via the kitchen pathway.
Once you're there, you'll need to blow up the broken wall in the screenshot below.
There's a pipe bomb on the wall next to the entrance to the room, so grab that, equip it, and throw it at the crack.
That'll knock the wall down and reveal some very useful fire for you.
Now, run into the closest pyre to push it towards the fire. Then, you can push the lit torch into the non-lit one so that they're both on fire.
After some clinking noises, that should complete the puzzle and let you interact with the coffin that was previous blocked off. Open it and grab what is inside.
It will be the Azure Eye, which you can combine with the silver key for something useful later on in the game.
There are more things to figure out in Resident Evil Village, so keep going and we'll do whatever we can to help you out.