Same instructions as original by @Ulysse98:

Make sure to print the case part with the front lip against the bed, and the tray on its only flat side (lip facing up).

The case part slides on the Audio interface from the front and should have a snug fit. The tray should be mounted with the lip facing away from the front. The case will slot into the mounted tray in a press fit that needs a little force to move. The case has a slight lip on the front face to stop the interface from sliding out when pulling a cable out, and the lip on the tray prevents it from sliding back as well.

Mount the tray using 2.9mm or 3.5mm width countersunk self-tapping screws of the appropriate length for your desk, any smaller and it might not hold the tray, and any bigger and the screw will not be flush with the tray and prevent the case from sliding in.

Printed on an Ender 3 V2 using 123-3d Jupiter white PLA, sliced with Cura 0.28mm layer height, 3 layer top, bottom and 2 layer walls. 15% infill, Cubic pattern.