These vents are a common frustration. Below is what I posted not too long ago:
The tech warned me about these, but I didn't try it until I got the trailer home.
Note that those tabs are on the moveable part of the vent, so they do move outward a very slight amount when they release.
I push the tabs (virtually) straight UP with my thumbs, both at the same time. Trying one at a time does not work for me. They feel like they are a friction fit to keep the vent closed.
On mine, when they release, there is no sound associated with the latches releasing; the vent just moves a bit outward.
Hope that made sense and helps.
Sherm & Terry w/rescues Steve (std Poodle) & Eydie (min Schnauzer)
2015 Jay Flight 27RLS (Camped: 102 nights 2015, 90 nights 2016)
2006 Ford F350 6.0 PSD, Lariat, 4WD, CC, LB, SRW, auto., Camper pkg.