Look for the 1/4" - 20 bolts.
They look like this. I bought these at Lowes.
If you print the attachment below, the screw will fit into it like this.
Screw the bolt into the tracker, and line it up so a flat edge is towards the spike with the LED.
Then gently slide the attachment onto it.
Unscrew it slightly, then push the bolt as far back into the attachment as possible.
If you do it right, the Tracker's LED spike will point upward when the attachment is on something.
(And on that note I just realized my attachment is on upside down in the photo. So, redo the last step :D )
Here's the STL. In the following link, I've included the large attachment shown above, which works for caps, bands, belts, and shoe laces, and a smaller one for attaching under smaller shoe laces...https://www.thingiverse.com/thing:3550999
Please let me know if you need any help! (ChiltonWebb at Gmail Dot Com)