I wish I could help you WAAA :"(

Try opening a 'LCD dead pixel fixer' site or video on bottom screen. I couldn't find any that works on the 3DS (JScreenFix is just stuck), but I hope this helps!

SONIC UNDERGROOOOOOOOUUUUUUND

I think you'll need to replace your screen. Not too pricey, but will require some patience and caution. I suggest looking for a professional to repair for you.

But of course, the price will depend of where you live

You have 3 options: 1: Put up a "dead pixel fix video", they might work but in my opinion they do almost nothing 2: Buying a new screen and repair it yourself (or get help from a professional) 3: Buying a new gamepad, will always work, but most likely expensive