Display is detached from corner

It sounds as though the adhesive holding the screen to the midframe has failed, unless the phone has experienced some sort of damage that could have bent the frame, causing the screen to detach.

Either way, you'll need to remove the screen and re-secure it with either a sheet of precut adhesive or a tube of glue such as B7000 for example. Here's a video showing you the basic steps.

One Plus Nord CE2 Display Replacement And Price

It frequently helps in removing the rear panel and the screen to heat the edges with a hair dryer or an iOpener to soften the adhesive and make it easier to take off. Once the part is off, you'll need to clean off the old adhesive with cotton swabs and 90% or higher concentration isopropyl (rubbing) alcohol.

Once you have the screen off, use a straight edge to check that the frame is perfectly flat; if it isn't you'll just be back in the same situation later on down the road.

As you work, take lots of pictures and once you're finished you can use those photos to create your own iFixit guide for those who come after you with the same problem! It's easy, fun, and will earn the appreciation of the repair community.

Create a new Guide - iFixit