I'll give you my standard "I'm going to open my phone up to fix something in it" response. DON'T.
Unless you've spent a few months learning how to repair cellphones, opening one usually results in breaking something. Then you open it again to fix that thing and break something else. By the time you admit that you can't actually repair it yourself (regardless of what the Youtube video shows - that's someone who's done dozens of them and knows how), you've spent enough on parts to have bought a new phone, it still doesn't weork and, if you're very lucky, you'll find a shop that will attempt to repair a phone you've been working on.
You'll pay for as many hours as it takes them to find out everything wtrong with the phone, so they can givve you a repair estimate. If you decide to have them repair it, it would probably cost a few times what a new phone would cost (they make a lot more than minimum wage, and the people who put the phone together in the factory make a LOT less), so they won't even repair it. (They'll simply buy or sell you a new phone.) But you'l still pay for the time the diagnosis for the estimate took.
It's a LOT cheaper to bring a phone that needs a "minor" repair into a shop and pay them to do it, than it is to attempt to repair t yourself. Even if their charge is 5 times what you can buy the part for. The "parts" for a toe to above the knee cast only cost a few bucks, so why does the orthopedist charge so much? (Because you won't lose your leg due to sepsis or lack of blood flow.) You pay for training and experience.
If you still want to forge ahead and fix it yourself, the first step is diagnosis - you have to determine WHY you have the problem you have. If could be a disconnected or torn cable, a broken connector, a broken circuit board ... There's no one single "this is always the cause" reason for the problems you're having, so no one can tell you what to do without having the phone in their hands. And unless you have enough experience and knowledge of electronics theory, that's going to be someone in a shop that you pay to fix the phone.