Bryce recorded his confession of raping Jessica, Hannah Baker, and several other girls and gives it to Jessica right before he's killed. Jessica makes a copy and the original is planted in Monty's stuff to frame him for the murder. Det. Standall destroys the original to cover everything up for Alex and Jessica, but Jessica plays the message for her group of friends so everyone is aware. At this point, the confession obviously won't do anything to affect Bryce, but it could bring peace of mind to the other girls he raped. I'm low-key hoping Jessica holds onto it and somehow shares it with those other girls or even Mrs. Baker. I don't know how much it would help Mrs. Baker, but I imagine it would be a comfort for her to know the real truth from Bryce himself.