Since the CORE One does not have a handle to slide the vent open and closed, I decided to create one. After I created an initial handle, I wanted to see if it was open/closed at a glance. 

I printed in PETG, though should work fine in any other material. Only supported the small handles, everything else should print fine without supports. 

No additional parts are required, though if you wanted to hold the top piece down a bit more you could use a small piece of command strip or double sided tape. It should slot into the vent fairly easily.