Can I use an iPhone 7 screen on the 7 plus to check if it works?

Unfortunately not, iPone 7 and 7plus screens have different connectors and they are not exchangeable. As for what you can do to fix it much depends on your level of skills in repairing electronics. To start with try to plug the iPhone into a Pc to check if it’s recognized by iTunes. You could also try shine a light to your screen in a dark environment to check if you have a backlight issue or get yourself a USB AMmeter to start verifying if the phone draws current or it’s completely dead. Without basic info it would just be pure gussing.