After installation open start menu and select MITOOL.exe
Connect Your OPPO A57 using USB with Your PC.
Turn off the phone,and the press all three buttons i.e, volume+,volume-,power on/off button while the phone is connected with the PC.(Ps there will only be black screen when you do this and nothing else).
U Will see that the Qualcomm drivers are being installed.(google how to install it)
NOW in the MIFLASHTOOL u will see com 10 or something like that.
IN The option above select the folder named OPPO A57 TWRP3.1.1 Recovery Toolkit .
AND CLICK ON FLASH. AND U WILL FLASH SUCCESSFULL.
DO NOT TURN ON YOUR PHONE. BOOT INTO RECOVERY BY PRESSING VOLUME- AND POWER BUTTON.
THE RECOVERY IS IN CHINESE. SO SELECT THE 7TH OPTION AND U WILL SEE SUPERSU ROOT CLICK ON IT AND SWIPE THE SLIDER FROM LEFT TO RIGHT AND THEN PRESS FINISH.
THE PHONE WILL BOOT UP NOW AND UR PHONE IS NOW ROOTED.THANK YOU !!GOOGLE SEARCH HOW TO UPDATE QUALCOMM DRIVERS.!!
mod edit - link removed ---- FOR QUALCOMM DRIVERS
mod edit - link removed --- XIAOMIFLASH TOOL.
mod edit - link removed-- OPPO A57 TWRP3.1.1 Recovery Toolkit.
After rooting is done install Xposed installer apk and follow the procedures (google it). And download this apk ColorOs 3.0-----
mod edit - link removed and select all the options as it is Chinese an now go to xposed And select this module in Xposed and reboot your phone. And its done the red flag won't be there anymore.
Thank you. If it worked for you please hit thanks.