⬢Now it is time to insert the PTFE tube back in. Note, that each end of the tube is different:
⬢One end of the tube has "rounded" outer edge. This end must be inside the hotend.
⬢Look at the other end, where the tube is drilled inside, the shape of the edge is "conical". This is the side, where filament enters the tube. This part must be outside the hotend.
⬢Push the black collet in. Slide the tube all the way in and hold it!
⬢Using the other hand pull the collet out and only then release the tube!!! THIS IS CRUCIAL for the hotend to work properly.