Pry off the back cover with an opening tool.

Take away the battery.

Peel off the warranty label.

Take away SIM cards and SD card if you have any.

Pry off the back frame with a plastic opening tool.

Take off the loudspeaker from the broken back frame.

There is no speaker on the new back frame.

Put the speaker onto the new back frame.

Press to set the speaker well.

Press clips to fasten the back frame.

Install the battery.

Fasten the back cover onto the back frame.

Source: Youtube