Please give me instructions how to flash and where to download appropriate custom ROM image for Android MLS phone . Current version on phone is Android 9 but company closed for good and phone does not update any more.
A "clean flash" refers to updating a ROM after wiping system partitions like the vendor, data, internal storage, and others. It's identical to a factory reset as it wipes all the data and saved settings from your phone, and after booting, you need to set up the device from scratch. It isn't as convenient but should go through without any problems.
#Note: Here's how to do the clean flash;
Start by booting your device to recovery and go to the Wipe section.
Then, wipe the following items.
Dalvik/ART Cache
Cache
Vendor
System
Data
You’ll need to also wipe the internal storage if you want. You should leave it if you don't have a backup of your phone's data or if you're planning to store the ROM files on your phone. If you're wiping the internal storage, transfer the ROM files to your PC or on a USB stick.
If you haven't erased the internal storage, flash the ROM files from it, but if you've wiped it, connect your phone to the PC with a USB cable, and the PC will be able to access the phone's storage. Transfer the ROM files to your phone to flash it.
If the files are on a USB drive, connect the USB to your phone via OTG connector, select USB Storage from the Files section, choose the files and start flashing.
Select the ROM from the Files section and swipe the slider to begin flashing. Don't interrupt your phone until it is done.
When it has finished, boot the ROM by tapping on Reboot to System. As it's the first boot after a clean flash, your phone may take more time than usual to boot up.
After booting, you'll need to set up everything as you do with a new phone, like signing in to your Google account, downloading apps, restoring your backups, and tweaking the phone's settings.