I just did this the other day, outside, at night, with only a flashlight, at -20 degrees Celsius. Good times.
What you will have to do is remove the bumper first. There are 4 black plastic poppy-uppy-thingies on top(I honestly don't know what they're called), 2 bolts behind the grille, a bolt and two plastic screws on each fender, and two plugs on the bottom that you have to use needle nose pliers to get off. Also, disconnect the wiring harness for the fog lamps at the bottom front centre of the bumper before you pull it off. It will take a bit of force, but a good pull on both sides of the bumper should get it off. I've done it by myself without issues.
Now, there will be 15 nuts connected to the bolts that are/were connected to the air deflector. There will also be 4 bolts/clips connected to the bottom of the air deflector. Take off all of these parts and put them in a safe place. I put my bumper back on at this point because my RA is my daily driver and I had places to be. Even with warm temperatures and water on the roads, I didn't have any issues with water in the intake(in my Injen CAI).
Take the air deflector somewhere warm and break out the sandpaper and epoxy. Sand down the areas where you need to reconnect parts, in this case the front left clips and more than likely the little angled connection at the bottom, and make sure the edges are clean. Mix the epoxy, I used Elmer's Epoxy, and place a light layer over the places where you're going to place the pieces, as well as a small layer on the piece itself. Hold the piece in place for roughly 5 minutes to let it cure, and then remix more epoxy and repeat with the other pieces. After this, store it in a warm,
VENTILATED area for 24 hours. I didn't store it in a ventilated area, my bathroom, and walking into my condo was not a pleasant experience. If you want, you can further reinforce the joints with more epoxy.
Now, take of the bumper once again, if you need to. Install the air deflector by making sure that all bolts go into their respective holes on the bumper, secure the centre bolt and work outwards. Be careful with the parts that are epoxied, because they can break again. Once you have reconnected all of the bolts, simply reinstall the bumper.
I hope that helps.