There is a dowel pin inside the hot block. Try not to let it fall out of the hot block.
Step 3: Use the 2.5 mm hex key to remove the two screws from the SuperPINDA sensor holder. Set the holder aside.
Step 4: Insert the Copperhead Hotend into the heat sink as shown. Use the 1.5 mm hex key to tighten the heat sink set screws circled in green.
Step 5: Use the foam swab to thoroughly coat the heater cartridge and the temperature sensor cartridge with Boron Nitride Paste. Clean any excess paste.
Step 6: Fully insert the temperature sensor into the top hole and the heater cartridge into the bottom hole.
Step 7: Reinsert the retaining screw into the hot block. Use the 2.0 mm hex key to tighten it.
Step 8: Replace the SuperPINDA sensor holder and use the 2.5 mm hex key to tighten the screws circled in green.
Step 9: Place the silicone boot onto the hot block. Make sure it is secured.
Step 10: PID tune the hotend and adjust the z-offset before printing.
This is the end of the Prusa Mini Upgrade Kit Installation Instructions.