These are a few 3d-printed parts to turn a small brushed micro quadcopter such as the Blade Inductrix and many similar ones into a hovercraft.

https://www.youtube.com/watch?v=4iPRBWFzJSU has a small demonstration of the craft working.

In order to do the same thing you'll need to print a bottom plate, a top plate, and two motor mounts for the top. You will also need a flight controller for brushed motors that can run the betaflight firmware, such as the BeeBrain flight controller I use.

Small modifications to betaflight are necessary to add support for a separate throttle channel input to separate forwards throttle from hovering throttle control. Those changes are available at https://github.com/rafl/betaflight/tree/rafl/hovercraft.

The two hover motors at the bottom need to be connected as motor 1 and motor 2 as far as betaflight is concerned and can be controlled with AUX channel 3 from your transmitter. The two top motors are connected as motor 3 and 4.