Help with headlight adjustment please

I've read the owners manual but still having trouble adjusting the vertical height of my headlights. I found where to adjust it, but there seems to be a white plastic cover preventing it from being adjusted.
Should the cover be removed? I tried removing it, but it didn't want to pop out and I didn't want to break something.

Thanks in advance for advice.
 
Here's a photo showing the plastic cover. There is a tab as part of the cover that prevents the screwdriving from adjusting anything.