Are you trying to save the kick panel??
I saw this last night, but didn't have the energy to do it justice!
Where the vent is, there is a large oval tube sticking several inches into the cowl.
It has a 3/4" flange all around the inner end.
Where it penetrates the cowl, it is sealed with some sort of thick sticky putty.
First, use a tool to pull the edge off the door pinchweld. I use a 1" putty knife, I heated it up with a torch and bent it 180 degrees, so I had a wide flat hook I can slide under the plastic and pop it off the pinchweld. Put some tape around it so it doesn't marr the paint.
Once that's off, you get to pull and tiwst and pull until the seal lets loose.
At this point, the kick panel will be flopping around and you'll think you're home free. Go have a beer, you are not home free. That flange is all that's holding it on, and that flange is considerably larger than the hole it must go thru, all the way around. Just work it, twist it, pull on it. Twist and pull at the same time. Have another beer. Be sure to cover your carpet so the blood doesn't stain it.
I trimmed the bottom inch off of mine, it made them easier to remove, and I was replacing them anyway.
1 kick panel is a 2 day, 6 wound, 12-18 beer ordeal. Your neighbors kids will learn many new swearwords. Don't throw anything. Don't break anything. It will come off.
Putting it back on is easier. Get the front and top of the flange thru the hole. Twist and push while YELLING as loud as you can. It will pop in.
Make sure you have enough dumdum to get a good seal. That area inside the car is a waterfall. Everything draining off the windshield or hood, down the cowl vert grille, pours down the sides of the cowl. That flange keeps the water from coming in the vent holes. The putty seals the tube to the cowl so the water can't get in behind the kick panel.
Poorly sealed kick panels are a main cause of wet carpet and rusted out floors.
Whew... I need a beer just typing about that Godforsaken ordeal. It's been several years for me, and thinking about the experience still causes me to break out in hives.