Release the cover of the PET bottle as well as the air could during the pressing free escape from the bottle. The mouth of the bottle put into the gap in the upper part of the press and push the bottom part of the bottle inside of the press.
Press the bottle between jaws of the press by pushing of the lever down. When it is too hard to press the bottle, check once again if the cover of the bottle is released enough.
Press the bottle by pushing of the lever until it reaches the down position.
Before releasing the lever of the pressed bottle, tighten the cover so as the released air could not come back into the bottle. The bottle stays in the pressed state.