In order to continue your adventure inside the Factory of Resident Evil Village, you'll need a special key. Here's a guide on how to find Heisenberg's key.
How to Get the Key
Before getting the key, you will have to get the mold. The mold is in a big case in the room just before the one with the horse crest on the door.
Melt Metal in the Mold
Unfortunately, you won't be able to open the door with the mold. You'll have to go back to the foundry, which is located on floor 4B of the factory.
To get to the foundry, you'll have to go backwards by taking the elevator with the Duke.
Take the elevator and go down to B3. Once on the B3 floor, make your way to the stairs on the far right (you can't miss the passage to the stairs, a Heisenberg creature will be waiting for you there). Go down the stairs.
Once the key has been molded, go back to the B2 floor to continue your adventure in the Factory.