The Android 10 rollout started on November 13 – 29, so if you have that, you can flash Pie back to it (back up everything - you flash a clean ROM and lose all your things). If you have Pie, there's no "earlier" one written for it. as Galactic Zoo said.
If you flash it back to Pie, it's going to update by itself anyway, unless you root it. (On a rooted phone, the update fails as soon as it finds root, it doesn't update. But you also don't get security updates to Pie once 10 is released.)