The author of this model is Stamos on printables.com. I arranged a print plate for the A1 mini and a fitting profile.

The RCA cover is printed upright, so its texture matches the walls of the case. This print in the pictures uses a 0.16mm layer height to get a nice finish. Combined with Bambulab PLA Matte Black it looks almost smooth. I also added rubber feet to keep it from sliding around.

The original model and assembly instructions can be found here here:

https://www.printables.com/model/24367-hifiberry-case

Assembly Instructions from printables.com

Place the 4 nylon screws in the holes under the case. Place the RPi board on the case matching the holes with the screws. Then screw the spacers. Because it is difficult to hold all 4 screws simultaneously, try one at a time. After all spacers are in place, take the 3D printed RCA cover and put it on the RCAs then mount the HiFiBerry DAC pushing it gently for the GPIO pins to sit. Then place the top cover.

There is an animation, to visualize the process, in the following link:
https://www.hifiberry.com/wp-content/uploads/2019/10/HiFiBerry-Case-Assembly.mp4?_=1
When you finish with the assembly of the player go to https://www.hifiberry.com/build/guides/