How do I change my jet black dyed hair to dark brown like I wanted?

It will have to fade out with a deep cleansing/clarifying shampoo.
Other than that you'd have to bleach it out and then put the desired colour on top. But I recommend you let it fade out. The more you wash it the more it will fade.
Also, a few members on here and had some success with fading hair colour with head and shoulders, so you could maybe try that.