Yesterday while my bike was on my cars biker rack the little preload dial popped off, how do i replace it ? last pic is what is suppoed to look like.

While driving back from my cottage the little black preload dial on my Specialized fuse 27.5 with xfusion shocks fell off. I want to replace it as it looks silly and am worrired about dirt getting into that little open top bit. I google replace this and that but couldn't find anything. Any suggestions?