What is this part and how do I stop it from rattling?

The plastic piece that is near the rear wiper. It's loose and rattles like mad. Any way to remove and make this more secure?

 

If you closely inspect the cowl, there is a gap between it and the frame. I added some foam pieces behind it and to the left. It makes the cowl fit more snugly and stopped the rattle when closing it.
Also add a few pieces behind where the spoiler touches the trunk door on both sides. It would prevent the paint from chipping and reduce further rattling.

 

I would take it off and see why it's rattling, may need new clips.

https://www.to4runner.net/removal-1369.html

 

Thank you. Found this also https://youtu.be/sWjS3jui_9s?feature=shared&t=38

 

Tighten it