Something almost all of us own already, coffee works great for going darker, resulting in a chocolate color without any damage.
Another simpler option is known as a coffee rinse:
Shampoo your hair then pour coffee over it (make sure it’s cool!)
Leave it for 20 minutes
Rinse with apple cider vinegar to help seal the color, then rinse with warm water.
If results aren’t immediate, repeat the process for a few days in a row to allow the coffee to penetrate.