To use:

Find an old reflector, not all will work. This is for a very specific one I had available to me. Pry off the reflect-y bit, and then press fit (use a drop or two of superglue if you like) into the corresponding slot on the middle piece. Then, put your AirTag in white side down, and clip on the back (use some force here, it can need some, and you can always reprint if you break it). Finally, remove the reflector backing from the piece that fits onto the seat mount, and clip in the assembly onto the seat mount bit.