It’s called the bezel, It’s plastic cast around a metal frame, used to reinforce the screen and serves as structural attachment between the case and the screen. It is adhered to the glass with what looks like industrial strength adhesive and the adhesive loops the whole edge of the glass to make a water resistant seal.
Also it is the sealing interface between the screen assembly and the case. Removing the frame is extremely difficult and there seems no reliable way to reattach a new one to seal properly.
You may need to cut open the metal bezel, remove a few structural screw holes, then try to dissolve the adhesive and cut along the display, refer to below video.
https://www.youtube.com/watch?v=syC-HJLjokI