Problem with the black plastic cover of the hinge.

I bought a case for my MBP 13″ but now I realised that the plastic cover of the hinge is a little loose, like if I forced it to take off the screen. So, now it makes noises every time I open and close the screen and the left side of the MBP looks loose too. I compared this with another MBP. Why this happened?  How can I fix it?

Thanks