Help assembling rubicon end caps - what is this part?

[JayDeadbolt]

So I bought a stubby steel rubicon bumper to put on my wife’s gladiator, and decided to also get a set of end caps to put on.
Problem is the end caps came in three pieces that I need to assemble. No problem, except there’s one part that I don’t understand how to install and mopar’s instructions are of course completely unhelpful. Hoping someone here can point me in the right direction.

It looks like I need a specific tool to do it but I can’t find anything on Google to help me.

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[Racerxtx]

You need a "plastic rivet gun" available at Harbor Freight.
Pic of it in the inset labeled "3X" upper right corner of your second pic.

 

[rohdawg]

Image 4 shows you exactly what you need.
You need one of these blind rivet tools.
They’re on Amazon and I’m pretty sure Harbor Freight carries them.

https://a.co/d/1tm7yf3

 

[JayDeadbolt]

Got it. Thanks guys.

 

[RubiDukkie]

I have the same tool that @rohdawg posted, but for those who don’t want to buy it, you can try this:

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