What is the rubber underneath the tabs on the display screen?

I am in the middle of a screen repair and during the removal of the adhesive, i accidentally removed the black stuff under the left tab. i'll attach a picture so that you can know what I'm talking about.

The repair went great other than that aspect and I don't want to return it to my customer without that piece. I think it's a cover for the speaker but i'm not sure exactly. If you guys know what it is, please let me know what I can do to replace it.

Thanks so much!