adi_adit, thank you for your informative posts. I've followed the service manual. I've removed just the screen from the device by undoing the 4 Philips screws that retain the sliding assy, tilted the screen forward and carefully detached the ribbon cable.

I now have the screen free from the device.

From the back of the device I have 6 screws. 2 have their heads missing. The top left and as predicted, bottom right of the metal back plate. The remaining 4 screws have had their screw heads significantly scrubbed. (Obviously the person who 'serviced' my phone used the same screws, although the service manual makes it clear to discard them and replace with M1.4x2.8 machine screws)

I've removed the remaining 4 screws (with great difficulty, they seem cross threaded). Detailing the screws shows that the thread is damaged. I've carefully removed the back of the display assy, and carefully removed the ribbon cable that attaches.

The remaining 2 screw threads that are stuck inside their holes have been broken off inside the hole, it would not possible to get any grip with plies on them either.

What are the next possible steps I can take to get the thread's out of their holes? Remembering that they, like the other screws are likely cross-threaded and the holes would need tapping out. (I don't have access to a tapper or a small enough drill bit)

Kindest Regards