unnlock a disabled iphone

can you use or unnlock a disabled iphone you have ben iven by friends who found one thats disabled its not a newer one but it works like nuthing worng with it and im good at fixing the screens and internal hardwear but idk how or if i can make a disabled phone work again cuz idk how to unlock it or find out whoit used to belong to but they give me phones all the time just im not able to eford new moutherboareds at moment as im only on disabilaty income it would be nice to be able to make some money of the old phones i got that where lost or stolen at some point and after being rehomed all the time found there way in my lap some had broken screens i bought new screens cameras charging ports its cost me to fix so can id at least like to make some of em useable again im sure someone i sell one too would also appreciate less costly working phone evean as a backup phone or somthing or a starter phone for there kids ya know lol