WARNING: YOU USE THE FOLLOWING AT YOUR OWN RISK. YOU MAY PERMANENTLY DAMAGE YOUR WATCH. I WILL NOT BE HELD RESPONSIBLE
I have extracted the ROM from the latest OTA update for the new LEM7 with the MT6739 ROM as, it appears, some people are awaiting the release of the ROM to update their watch because it may be rooted, may lose valuable data, settings and apps, etc. or they may want to root and/or install TWRP etc. for the ROM update.
I updated my watch OTA to V1.5 and worked out how to extract the ROM. I have trialled it by down grading my watch to V1.2 and, using extracted ROM, updated it back to V1.5 successfully.
The problem was that I lost all my data, my settings and my own apps (they were wiped in the update but I had previously backed them up with My Backup Pro and downloaded them to my PC where I could restore them).
During the OTA update I noticed that only the System appeared to be involved so I downgraded to V1.2 and updated it to V1.5 by only installing the System partition of V1.5 and it appears to have worked and I did not lose any apps, settings or data.
Since I only updated the System partition, the Boot and Recovery partitions should remain untouched and the updated ROM will still have root and TWRP. I have not trialled this though.
The Security Patch, Baseband and Build No were updated when only updating the System partition, the Kernel was not updated though.
With the extracted ROM you now have access to the Boot partition to root with Magisk and the Recovery partition to port a TWRP into.
I used SP Flash Tool to flash the stock and extracted update ROMs
I uploaded the extracted OTA update ROM V1.5 to Mega here:
mega.nz/#!8Dw3lYSa!PwZrPFzhDUAHmmfG5TC68vg8jPA096icWv847ulYhng