Let us assume I have a severe problem with the most current version 1.21 and I would like to return to the previous stable 1.20. All that is offered is to ‘Export Update’ or to ‘Delete’. How can the previous version be installed again?
(A friend of mine with an ePhone and not experienced with technical issues recently updated the /e/OS, but the SIM card no longer can be unlocked. So we would like to fallback asap if possible).
Export could be a good option to move it
to a physical SDcard or
to an accessible part of the internal storage
Then you are supposed to be abble to install it from the recovery-e
Keep in mind that with installing an OS build with an older security patch level Android rollback protection is supposed to force a factory reset to boot successfully, wiping user data.