My phone is bended how to repair it

Aman, it's hard to say exactly what it will take to fix your phone without a better idea of the damage. Adding pictures of your phone to your question pointing out where it's bent would help us a lot in figuring out the best way to get your phone back to normal.

In general, though, the midframe housing that holds the internal components is readily available as part of a screen replacement; I didn't locate anyone selling just the frame by itself without the LCD, but an extensive search could turn one up. However, what I'm referring to is something like this, where the LCD comes already attached to the midframe so all you have to do is open up your phone and move all of the internal components to the new screen+frame assembly.

OEM LCD Display+Touch Screen Digitizer Assembly Fix For Xiaomi 4 mi4 Mi 4 Black - eBay

Of course, this one is for a black screen so it may not be the same as your phone; as far as I can tell it looks like it comes in white too. However, if you're replacing the screen and are okay with changing color, then it will work just fine.

There aren't any guides available for just replacing the midframe, and the screen replacement guides I came across are mostly for separating the LCD from the midframe and replacing just the LCD, which isn't what you want to do; in your case you'll want to replace the LCD and frame as one assembly.

I'd suggest using the iFixit screen replacement guide, but stop at Step 8; there's no need to separate the LCD from the midframe if you're replacing both. You will, however, need to carefully compare the gutted original phone to the replacement assembly and transfer any remaining parts to the new screen.

Xiaomi Mi 4 Display Assembly Replacement - iFixit Repair Guide

Good luck; add some pictures and let us know how it all turns out!