The cover of the K400 plus and non-plus are different and I couldn't find any models for this specific one. Seemed like a good beginner FreeCAD project, then I realized this thing has literally just one non-curved surface…
This is meant to be printed with a slightly flexible filament - PETG recommended. PLA may work, but the front hooks are pretty flimsy and may have a lower life.
The model is easiest to print on the flat back surface, though this means the mounting hooks print in the weakest layer orientation. In this orientation the print requires no support structures. It appears to work for me, but if you want to take your life in your hands you can try printing it standing on the side (with a lot of supports and a brim).
The author marked this model as their own original creation.