You can fold the Joolz pushchair in several ways.
One way to fold it is to set the handlebar in the lowest possible position. You can do this by pushing the silver pawls on the inner side of the handlebar downwards. You push the grey buttons at the bottom of the handlebar and slide it down in order for the handlebar to shift completely in the case. Make sure that you don’t push the pushchair! When the two plastic parts touch each other you know and feel that the pushchair will fold itself automatically.
If you can not manage that, you can also try to fold it using your stomach. First set the handlebar in its lowest position. Then press the grey buttons at the bottom of the handlebar and push the handlebar with your stomach. The handlebar slides in its case and the handlebar will fold automatically.
You can see a video in the links below explaining how to fold the Joolz Day pram here as well.