Follow the instructions to use the MSMDownload Tool for your model of OnePlus phone.
This will wipe the phone.
https://www.thecustomdroid.com/oneplus-6-6t-unbrick-guide/
Scroll down to view the Unbrick details and downloads.
Download the correct version for OnePlus 6 model you have and use the Android version you want TO use to unbrick the phone .
Once you have the phone backup and running.
Install OTA updates to get the most recent update.
If you are not comfortable doing that, please contact OnePlus directly at the link below for more information. Or bring the phone to an approved OnePlus service center.
Scroll down the page for contact details.
https://www.oneplus.com/supportClick to expand...