Apply a non-corrosive non-solvent lubricant/sealant. I used Armor-Dilloz Bead Buddy because I had it, worked great. Dish detergent would probably work well enough. Don't use a grease like faucet lube as it won't ever set, and so the stem will spin when you tighten or loosen the cap.

Insert the stem from inside the wheel. Screw a valve extender onto the stem and use it to pull the stem until it pops into place.

Remove the valve core and set it aside.