I have a 2012 chysler 300. I accidentally dropped a pen down one of the vents , second from the driver 's side. One in the middle now it only blows hot air from two vents, the passenger side vents

The pen has blocked one of your blend doors. The only way to fix the problem, will be to tear the dash apart. Unless you buy one of those flexible claw grabbers and stick it down the vent. You may get real lucky and get the pen out,or at least knock it out of the way.

Wrap up some duct tape around your hand, sticky side out, and fish the pen out. If your hand isn't long enough find something that'll snake down the opening and wrap that in tape. Be careful on what you jam down there, the pen is likely blocking the blend/mode door from moving, but you don't want to actually break it because then you will have a laborious job getting to it.