>How

the most a noob can do with it is to remove the crud using alcohol and a toothbrush

if you had a voltmeter, you could beep out various traces to see if they're broken

as for actual repairs, you need someone who has the tools and skillz
take it to someone who does phone repair.
someone like www.youtube.com/@NorthridgeFix will charge $90 just to look at it, so you may be better off replacing it