Why is the side of the phone not working?

I am reading your question as saying that part of the touch screen isn't working but part of it is, is that correct?

If that's the case, the only real solution is to replace the entire screen; phones are no longer made such that the touch screen can be replaced separately from the LCD. I'm afraid iFixit doesn't have any guides for you, but there's a Spanish site called Nadie Me Llama Gallina that has just the one you need.

Manuales / Nokia 3 / Fullscreen

Fortunately for you, the price for a replacement screen on your phone is dirt cheap these days; the first one I ran across on Amazon was under $10 USD! It's also available on other major sites like eBay and AliExpress.

Amazon.com: LCD Display Touch Digitizer Screen Assembly Replacement for Nokia 3 Black TA-1032 TA-1020 TA-1028 TA-1038 : Cell Phones & Accessories