Warning: Make sure to download exact firmware for your model. You can discern your model from Settings > About phone > MIUI version (Eg: In MIUI version V13.0.6.0 SKHMIXM ‘MI’ represents your phone region, which is Global). You can also verify your Xiaomi phone at official site.
Tip: Some devices might have buggy USB support while in bootloader mode, if you see fastboot hanging with no output when using commands such as fastboot getvar ..., fastboot flash ... you may have to try a different USB port (preferably a USB Type-A 2.0 one) or use a USB hub.
  1. Extract firmware files from zip 
    unzip -qq miui_*.zip firmware-update/*
cd firmware-update

  2. Power off the device, and boot it into bootloader mode

  3. Run the following commands to flash firmware: 
    fastboot flash abl abl.elf
fastboot flash ablbak abl.elf
fastboot flash aop aop.mbn
fastboot flash aopbak aop.mbn
fastboot flash bluetooth BTFM.bin
fastboot flash cmnlib cmnlib.mbn
fastboot flash cmnlibbak cmnlib.mbn
fastboot flash cmnlib64 cmnlib64.mbn
fastboot flash cmnlib64bak cmnlib64.mbn
fastboot flash devcfg devcfg.mbn
fastboot flash dsp dspso.bin
fastboot flash hyp hyp.mbn
fastboot flash hypbak hyp.mbn
fastboot flash imagefv imagefv.elf
fastboot flash imagefvbak imagefv.elf
fastboot flash keymaster km4.mbn
fastboot flash keymasterbak km4.mbn
fastboot flash storsec storsec.mbn
fastboot flash modem NON-HLOS.bin
fastboot flash qupfw qupv3fw.elf
fastboot flash qupfwbak qupv3fw.elf
fastboot flash tz tz.mbn
fastboot flash tzbak tz.mbn
fastboot flash uefisecapp uefi_sec.mbn
fastboot flash uefisecappbak uefi_sec.mbn
fastboot flash xbl xbl.elf
fastboot flash xblbak xbl.elf
fastboot flash xbl_config xbl_config.elf
fastboot flash xbl_configbak xbl_config.elf
  4. Reboot: 
    fastboot reboot