Ok I am a total novice in gaming plus we're abroad so I may get some terms wrong! 
When playing Minecraft (and only Minecraft apparently) my son's left (blue) joy con isn't working properly- when he wants to move left it goes right and up goes down. It only appears to be that which is wrong.
Ive gone into settings and reset to default but it hasn't helped.
Google is useless.
Any ideas? He's so frustrated and doesn't want to play anymore which is a shame as he was just getting into it.