You can boot into fastboot mode of C21 by executing this command through PC or a laptop.
1)Download Adb and fastboot drivers. (Skip if done)
2)Go to your device and enable usb debugging.
Then do this-
- Connect your phone to your computer using a USB cable.
- Open CMD/Powershell on your computer.
- Run the following command to make sure the computer recognizes your Realme C21:adb devices
- Now you have two choices again:
- If you want to boot your Realme C21 into Fastboot Mode, use the following command: adb reboot bootloader
- If you want to boot your Realme C21 into Recovery Mode, use the following command: adb reboot recovery
Once you run the following commands, your Realme C21 will turn off and go into Fastboot/Recovery Mode. That is all you have to do. Now you can flash factory images, custom ROMs, unlock the bootloader, and much more.