The side vents should be held on via a tab and clip. When I first took delivery of my Levante, 3 of the vents were loose so I removed it, inspected the clips, and reinstalled it. If I remember correctly it's a slide forward facing portion first which is the tab that holds the front in place and the rear is the tab that just has to "clip/pop" in. When the dealer's service techs receive and prep the car from off the truck, I would've expected this to be one of the things they inspect before delivering the vehicle to a client, but apparently not.
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From here, enlarge the image of the rear of the vent and you'll see the tab and clip I mentioned above and below.
Before you do this, please remember you're doing this at your own risk and am therefore not responsible if something goes wrong. My instructions work for me as I work on cars quite a bit so I'm experienced in removing parts, panels, etc. and I know the general concepts of how to remove these sort of things. Always use caution and less strength is usually better than brute force as you could damage your paint or break the part. If in doubt, you can always take it to the dealer or your local performance car shop or body shop. Or alternatively, if you have a friend experienced in cars in general you can have them help.
Notice that there's 2 metal portions on the backside. There's one that's at somewhat of a 90 degree angle. This is the tab that is towards the front. The other side is a metal clip. What you'll need is some painters tape or masking tape to protect the paint and my preferred tool is a plastic trim removal tool rather than a metal screw driver or metal pry tool.
1. tape the rear side of the vent on the vehicle paint. I usually put 2-3 layers just to be safe as 1 layer could tear while your push/pry with the tool.
2. use the trim tool to get underneath the rear of the vent to separate it from the fender. Here you have one of two choices. you can gently twist the tool so that it slowly pries the vent away from the fender as your other hand helps by gently pulling. the other method is to not twist the tool and if you have enough separation already with the tool laying flat underneath the vent, you could pull with your other hand. If you're twisting to help get the clip free, the vent could just pop out which is why the other hand is there to help hold and guide. If you're using a metal tool like a micro flathead, do not twist as you will dig into your paint. Just get enough of the tip under the trim, place your index finger between the screwdriver and the fender to act as a leverage point basically creating a teeter totter like effect, gently push the rear of the screwdriver towards the fender (make sure you have tape here just in case that rear hits the paint), hopefully the flathead doesn't slip and scratch the vent or paint. I suppose you could use this same method on a plastic tool and it'd likely be safer given less contact with the paint means less opportunity to damage the paint.
3. as you're slowly pulling with your fingers or prying it out with a tool, as enough of the trim starts to come out, you could potentially use your tool to help press the clip in enough to make the pulling easier.
4. once the clip is free, just move the vent towards the rear, it should clear the front tab.
To re-install, just slide the front tab under the fender all the way, then gently press the rear till you hear it pop in. gently jiggle it to see if it's firmly in place.