Please help me out! I want to fix my old Dell Vostro 5560 screen

You should check your battery first. Check in Settings > Battery > Battery Health > Maximum Câpcity. If it’s more than 80%, you should be okay. If it’s under 80%, you’ll need to replace the battery If you have iOS 10 or earlier, search on App Store for Battery Life, and download it, run app and see if it’s more than 80% or under 80%. Again, if you have the battery under 80% or lower, swap it ASAP. Hope this help you! :)