MsmDownloadTool V4.0 International (Oxygen OS 5.1.5)
May 2018 Android patches
Guide how to revive your op6:
First of all, you need to access to fastboot mode, if you can't , contact Oneplus support, then have a windows computer and download these file and drivers qualcomm ( https://androidfilehost.com/?fid=24052804347798730) and extract in one folder.
After you have all the file ready, plug in the phone to the computer, go in device manager and under port (COM) disinstall qualcomm one (oneplus 6) and then unplug.
Now you have to go in Windows test mode to not let him install default drivers, so:
windows key (on keyboard) + X, windows powershell (or normal prompt) administrator and write and enter: bcdedit /set testsigning on ( you will repeat the same process with "off" to stop the test mode after you will finish to do all the things).
Reboot the system and you could see in bottom right corner the test mode, now you are ready to install properly drivers.
Power off the phone, then hold for 5 seconds vol up and plug the usb to computer. Now you have to see US8_BULK as new device connected and you can also see in device manager; if you can't notice it, repeat the process until you see it (power on, power off, hold...) there is a full youtube guide for op5 and it's the same process (https://www.youtube.com/watch?v=PpLvmID1wdI)
Right click con US8_BULK in device manager and update drivers by system files (go to the folder's drivers you had extracted before).
Now you should see qualcomm drivers under port (COM).
You are ready to let the tool to do all the stuff, so let plugged the phone, always powered off, right click on msmdownloadtool and execute as administrator.
You should see your device and click start to begin the process; if it gives you some error (like sahara or something else), unplug, power on, power off and the plug it again, now it should be fine.
And that's it, the tool will do all the work and, at the end, you will have like a brand new phone ready to a new setup.
EDIT: if you are stucked in bootloader, you have only to power off and continue with the part: ... hold for 5 seconds vol up... (it happened in page 4)
Please, consider to donate me something for the work and the risk (maybe idk). Thanks
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(Thanks to @nytebird for the contribution)
If you want to buy another Oneplus 6, this is my referral to have 20€/$ discount on accessory: