Canon DP-V3120 Service Manual page 82

[Note on disassembly ]
Position determining
convex area
As there is a convex area to determine the position of the bezel unit, it is less likely to come off.
After removing the screws, remove the BCKBTM unit, trying to push the unit upward.
Page 29
[Note on assembly ]
Make sure not to have it
extended beyond the extended beyond the
convex area to determine
the position.