There is a LineageOS page for upgrade instantnoodlep of firmware here Update firmware on instantnoodlep | LineageOS Wiki
This method suggests one gets the firmware with the third party app Oxygen Updater, but note that you are not fully reverting the device to stock ROM so at this point you are not deleting any data.
One can check if the /e/OS downloaded ROM appears to contain firmware parts by running payload-dumper-go on the downloaded ROM. One could follow this Walkthrough, but run payload-dumper-go with no -p option so that all partitions are extracted.