Place the blade into the plunger from below at a 90-degree angle to the cutting direction.
Twist the blade until the teeth face forward and it sits securely in the guide roller groove. i--- Bosch Pst 54 Pe Manual
Turn the screwdriver counter-clockwise (left) about 3 to 4 turns. Place the blade into the plunger from below
There is a hole at the top of the plunger (the rod that moves up and down). Insert a long screwdriver from above into this hole. i--- Bosch Pst 54 Pe Manual
If you are looking for the official documentation, you can view the Bosch PST 54 PE Manual online or download it as a PDF.