You can open it with your fingers.
Pic 1) open the front vent
Pic 2) see that small insert in the center? put your finger in the bottom of it and push down.
Pic 3) That open slot on the right is what your finger is pushing into.
The filter panel just pops right out.
Pic 4) I bought some filter material, cut it to fit and inserted it into the return air area. It works great and doesn't restrict the air flow. $6 and I had enough material to make about 8 filters.
https://www.lowes.com/pd/Filtrete-Co...ilter/50124672
The filter material is about an inch thick and cannot suck into the return air.