This is a DIN Rail ABS Case for Raspberry Pi 4 with Large Inner Space and manufactured using Injection Moduling.
1. press the rail lock by forefinger, then push it out by thumb as the picture shown
2. remove the bottom panel from the main part
3. fix the Raspberry Pi onto the bottom panel by screws
4. put on the bottom panel, aligning it with the buckle and USB connectors
5. snap another side
6. insert the rail lock (note the different sides, don't be upside down)