@14v3nd3r I have an opo myself. I use the installer to reflash when I screwed up. My main problem was getting the right usb driver installed.
I think what the installer does is first install a new recovery (the UBports one) with fastboot and then with this new recovery install UBports itself. Therefor it uses the fastboot and adb utilities it also installs (I gave you the path for windows).