So, here are the steps to do a no kidding hard reset on your GoPro 4 Session.
- Remove the SD card and insert it in your computer
- Format the SD card
- Add the two files below to your SD card
- Insert the SD card back in your GoPro 4 Session
- Push the “RECORD” button and wait about 8 seconds
- Watch the indications on the LCD that the GoPro is resetting (this will happen by itself after the 8 seconds wait)
- Remove the SD card and format it again
- Insert formatted SD card into your GoPro and now your camera is like brand new
Hope this helps.