You need to dl that app from oneplus forums. Its ment for rollback mainly. It can easilly be found at ob thread. But no idea, try that app if that works. Sure you need to dl full ob1 first. https://forums.oneplus.com/threads/...-for-the-oneplus-9-and-oneplus-9-pro.1502946/So i flashed the ob1 stock boot image and rebooted to system. updating via system update and for some reason it keeps saying installation failed. Any ideas why? How did you go about flashing ob2 since theres no local upgrade feature?
That app is in that op also