Part of the touchscreen does not work

My Bluboo X550 is almost new, but today it fell from 3ft on the ground.

Afterwards, the bottom part of the digitizer didn´t work anymore. I googled that and found out, that the LCD flex cable could be loose.

Here a picture, where you see the LCD flex cable:

https://i.gyazo.com/4e9322228228845435e7...

But I don´t know, how to detach the display from the mainframe to see, where the cable goes. I already plugged it out and in, but nothing changed.

Furthermore, it doesn´t seem so easy to remove the mainboard, without damaging the soldered cable for volume and power buttons:

https://i.gyazo.com/c7cdc1e32f9c23010e89...

Can anyone help me? I don´t want to send it back to China...