You have to unscrew the seven highlighted screws with a philips screwdriver

Note that one of the screws may be hidden under a Xiaomi Label sticker

Now with a pair of tweezers or with a prying tool you can gently lift up the plastic shell from the phone. Try not to force any junction but gently move it until you find it loose.

After removing the plastic shell you can also unplug the ribbon cable of the touch sensor. Do it as shown in previous step.