iPhone screen making clicking sound & bottom of screen not 100% flush?

Got this iPhone 6 in with another iPhone and was planning on selling it off as I didn’t need it. I checked that everything worked etc. When I took the case it came in off (Tech21) I noticed that the bottom right corner makes a clicking noise when pressure is applied in the bottom right area, and the bottom part of the screen that screws into the frame near the charging port is slightly raised and when pushing down makes it flush. I have tried opening, applying pressure to the bottom and the re-attaching the screws and that didn’t work. I checked the display and it doesn’t have any stickers or anything and the inside is perfectly clean so it is either original or has been well repaired. I am wondering if anyone had any ideas to keep the frame flush and stop the clicking noise when pressed down. Would using a iPhone 6s adhesive frame gasket work at adhering the bottom of the screen down to the frame? The top half of the screen sits perfectly (FYI). Thanks in advanced!