How to fix the streak of vertical line on my print?

Wipe clean the printing head, that should fix the streak right away.

Before you clean the printing head, please wait for 10 minutes after you turn off your Cubinote to cool down the printing head.

Please also be careful of the sharp blade on the printing head.

Here are the parts of the printing head that you need to wipe.

Here's how to correctly wipe the printing head.