To properly remove the regulator knob for cleaning, start by pushing down on the knob and turning towards the "Clean" position. This may require a little bit of pressure but should not be a struggle. Once the knob has turned to the "Clean" position, you can lift it up and remove it. 

To properly replace the regulator knob after cleaning, align the dot on the “Clean” position on the knob with the dot on the base. Drop the knob into the lid and turn it towards the "Pressure" position. 

This article can also help with the following issues: remove, replace and clean pressure valve