I wanted to add a HEPA filter to my auxiliary fan but did not want to take apart the fan to install magnets. I also had extra filters from the ones I installed on the chamber fan and wanted to use the same filters for both locations. I created a filter cover that magnetically attaches to the screws that hold the fan in place. I only have two screws holding my fan secure, the third location did not have a metal screw. I printed this in ABS for durability. I did not realize until after making this that the auxiliary fan doesn't run when I am printing ABS, which is what I needed it for. So I have been turning on the chamber fan at 20% when I print ABS to filter the air instead. I downloaded one that fits on top of the charcoal filter.

To install the HEPA filters, I cut off the ribbon tabs and fit two of them into the open spot. Here is a link for the filters I used:

https://www.amazon.com/dp/B0782T7L6P?psc=1&ref=ppx_yo2ov_dt_b_product_details

I also used two magnets in each hole so they are strong enough to hold this in place. The magnet holes are designed a bit small so you can friction fit the magnets in place. Here are the magnets:

https://www.amazon.com/dp/B084VGP2LY?ref=ppx_yo2ov_dt_b_product_details&th=1

It's been working well so far allowing enough space for the bed to move up and down.