its just 8 empty bits at the bottom (all numbers zero)
in a digital transfer recorders dont lock on bit depth, only sample rate.
easier to switch the recorder to a 16 bit file before recording, but if you have 16-bit data dumped into a 24 bit files, use bit depth reduction in a wave editor to knock it down to 16
do not use any sort of dither, this will create distortion. you want to simply truncate the data and chop off the empty 8 bits.
if your wave editor does not offer bit depth reduction with simple truncation, you can probably do it on the command line with something like ffmpeg