I didn't crack the screen or the back panel of the phone I chipped the middle part of the phone that goes around the phones edge. would that be the midframe??
and also how to fix or is that part replaceable
Yes that would be the midframe, but replacing this would be very difficult, as the screen is bonded to the frame, and removing it without breaking the screen is a hard task, even for professionals.
who would be able to do it if I bought the midframe
You would have to go round and ask shops if they have experience, a lot will either charge the price of a new screen (due to risk of breaking the screen during removal) or they will straight up not take on the job, you may be lucky and find someone who is experienced enough to try take on the job, but even then, they will probably warn you about the risks.