Moving back to an older version of OxygenOS.

If you are trying to or change your phone's region (e.g., ColorOS to OxygenOS), let me know the exact model number (like NE2211 or NE2215) and I can look for the specific guide for your version.

Manually switching between regional firmware versions (e.g., ColorOS to OxygenOS). OnePlus Community Alternatives and Community Workarounds

Some versions require a login. Use the default credentials: