This is a small cooling duct for the original fan that comes with the  Ender 3. You just need to remove the original fan duct and put this one in its place. Ideally printed from PETG as it sits very close to the hot end, but my PLA one has not melted even printing PETG for 8h. As the channel through the far side of the duct is very small, it's important that the printer is not stringing, or you'll end-up with uneven airflow.
Probably only works with the original hot-end as it's touching the padding around it.
If you've removed the padding, I recommend wrapping the duct in kapton tape to stop it from melting.
Hope it's useful, as it's been working well for me.

http://www.petsfang.com/
What to print
Shortcuts to the current  Creality & Tevo "Files to Print" Docs is below. This takes you to an interactive spreadsheet with links to the individual files needed:
http://www.dpetsel.com/files2print.html  
Addded a couple of modular RH mounts for 8 & 12mm Inductive ABL's. The compression type has a nut and a screw to hold the probe in place (similar to the Prusa Pinda type mount) Example in the picture below:
Micro Swiss Direct Drive Files here:
https://www.thingiverse.com/thing:4775320
It was brought to my attention by Всеволод Меренков that the clip area on my All In One Blokhead bases were a little long causing clearance issues to the backplate. I have modified all those bases and the new files are up. If you have printed the old files you can just cut out about 2mm from the side clip at the bottom to get it to fit. Otherwise just print the new base files. Sorry about that. Dave 2.12.21
1.17.21
After much research, it appears the Ender 3V2 was delivered with 1 of 2…