Instructions
Download the appropriate package - OnePlus 5 or OnePlus 5T
Open the File Manager and move the downloaded .zip package from the Downloads folder to the root directory.
Open Settings - System - System updates, press the cogwheel on the top right corner, choose the Local upgrade option, and select the rollback file.
Users who are still on OBT builds for 5/5T can update to this build only via update from recovery. For those, PLEASE NOTE, your entire data will be wiped.