I had a GoPro Hero 4 Black sit at the bottom of the ocean for three days in a leaking waterproof case until a diver friend retrieved it for me.
Amazingly, I was able to get it to power on.
But I did the following first:
- Dismantled the GoPro immediately and washed all components in isopropyl alcohol.
- Ensure that all traces of corrosion (white) were washed off and that all metal contacts were clean
- Let the components dry for several days
Now the GoPro didn't work 100% and required some parts to be replaced.
- HDMI output
- Lens & sensor
- Power and WiFi/Setup buttons
What didn't work:
- Some of the LEDs
- The LCD display
- The shutter button
- The SD card expansion slot
- The battery (it swelled and oozed)
Considering that your GoPro was only submerged for 7 minutes, chances are that yours is in better condition than mine was and so you may be able to salvage much of it and even possibly repair it to fully working order.