Since Electronic Boggle has been released in several versions (Hasbro 1990s, 2000s, Touch, Flash, App), the mute method varies. Try these in order:
Check the back/battery compartment for a code like Boggle Flash, Boggle Reinvention, 40210, etc. Search "[Model] manual PDF" or "[Model] mute sound".
Common Models:
If none work, the unit may lack a mute function—common in 90s/00s handhelds.