How is it bent? As in the entire case? It basically can't be repaired. Maybe a third-party might try, but it isn't likely to be reliable. You really don't want the glass popping out. The case keeps the glass in, you could end up with the digitizer acting up.
This was where a previous posted got the price. It's called a "repair" but it's really just a "broken iPhone trade-in".
iPhone Repair - Official Apple Support
If you really want to try, you can look up various home-brewed glass repairs on YouTube.