This fell out. Any idea on how I get it back in?

 

I used an Allen key to apply pressure on the pin

 

If the push pin is no longer holding it, get a new one. When I had my bed liner done, they took them out which ruined the pins. I got some new ones at lowes and it’s been fine since October.

 

Oops wrong thread :

 

Any suggestions on the push pin to buy. There are thousands available on Amazon in packs of 20 - 100. I just need one, and the right one.

 

Go into Lowes or someplace similar like I mentioned. Bring your pushpin and match it to a similar one. I don’t remember the ones I bought. They were not exactly like the oem,
but worked just the same.

 

Most parts stores will also stock a replacement

 

OP, your part number is Ford N804570-S. This is a common fastener. You are probably missing the nylon screw that goes in the centre and expands the other piece holding it in place. Use a ½" long #6 sheet metal screw or drywall instead. It will do the same thing.