You can directly update or downgrade through smartswitch application through your pc if new software is available. You need pc to downgrade or update, or you can do it from nearby samsung service center

First You have to downgrade to 8.0 after that you will get the 8.5 stable update. This will reset your device.

Check the usb cable or if possible try with other usb cable

​"That's correct. This appears to be a significant software issue on Samsung's end, but the company doesn't seem to be acknowledging it. It's a widespread problem reported by many users, but unfortunately, Samsung is ignoring the issue and the custom...