Hi, have formated my device now have no IMEI
There's a permanent two row watermark on the top of the display, some Chinese writings followed by
tee key
google key!
Would really appreciate some help

There is a way to remove the watermark by uninstalling factorymode:
adb shell
pm uninstall --user 0 com.mediatek.factorymode

Source:
https://www.youtube.com/watch?v=SDSQGBEK6wY

As for the IMEI change, it happens rarely after flashing, but there is an app for that: IMEI Generator or IMEI changer (IMEI number should be 15 digits, generated by luhn algorithm)