LOL, not so reliable now. (sorry about the joke)
Can maybe flash different partitons back manually, but might be better to try and push install of service rom.
try this: copied from telegram support group.
Service rom BND-L21C432
https://www.androidfilehost.com/?fid=11050483647474828964
1. Unzip download
2. copy the dload folder to root of sdcard
3. power on phone holding all three buttons
4. After phone finishes and reboots, unlock frp and bootloader, if needed
5. Use Huru or HWOTA to flash correct firmware for your model/ region.
As with all mods to phone. This is un-official and not guaranteed to work same for you as it has for others.
This method has been confirmed as recently as yesterday.
It is also possible that additional steps may be needed to finish the process. Depending on the current condition of device I suppose.
One recent report of using service rom lead user to need to fully downgrade to nougat rom before correct build number and version was shown in about phone.