Any way to close the safe mode?

[AC Question]

I used Samsung Galaxy Grand 2 for about 2 years. Then it got problem that my volume down button is keep holding but the really big problem is when I restart my phone I will turn on OS install mode it say
Press volume up: continue
Press volume down: restart the phone
But I can press noting. It still stuck on this page only way to open my phone is hold power button and volume up button to open on safe mode and my app is not working in this mode and when I tried to close Safe mode it open OS again and I have to open in safe mode again.
It think the OS install mode open because my volume down button is stuck but no idea about why I can click noting.
I go to Samsung and they said the mainboard is broke and it cost about 3000฿ (about 100$) to fix it.
So now I'm hopeless and want to find a way to fix it myself. So I need the way to fix it such as disable the volume down button.
Remember that I can't open any app so don't find any app for me.
Thank you so much
P.S Sorry about bad english I'm Thai

 

[Tim1954]

If you gently take the back cover off the device, there are some screws holding it on, carefully undo them and pull the back off very carefully. If you can actually see the microswitch, blow it out (you can get canned air from electronic shops) in case there's dust in contacts, perhaps spray some contact cleaner (if it's available there) and put it back together carefully. If that doesn't work, the switch may need replacing... This is assuming that it's the switch and not some fault in the circuitry, ideally you would do measurements to confirm, but in desperate times this may be worth a try... Good luck! If you don't force things you shouldn't damage anything...