The focusing screen is located inside of the body, at the top of the opening, directly above the mirror, inside of a metal housing.

To remove the focusing screen, first use tweezers and grab onto the latch that secures the housing above the mirror.

Then gently pull down on the latch, towards the mirror, to release the housing which contains the focusing screen.

Using tweezers, gently but firmly grab the focusing screen by the outer tab, and lift it out of its housing and the camera's body.