The small form L12 case can be fiddly to open. Here's how.
The Avance L12 chassis is a compact desktop case able to take a regular mATX motherboard and full height IO cards but its clever design can sometimes make maintenance a little fiddly.
The assembly and service guide is attached. This details the process to open the case are included in the attached PDF document.
The below video shows a disassembly of a computer built with the L12 chassis in order to service the power supply.