If you go to:-
https://www.tohodo.com/autofill/help.html#other
at the bottom of the page there is a 'Tip':-
TIP: You can customize the sound effects by replacing sound.ogg with
your own audio file. On Windows, sound.ogg is located in
%USERPROFILE%\Local Settings\Application Data\Google\Chrome\User
Data\Default\Extensions\nlmmgnhgdeffjkdckmikfpnddkbbfkkk\{version
number}. If you're using Mac or Linux, then try searching for
"sound.ogg". There are two requirements for the audio file: (1) it has
to be in Ogg Vorbis format, and (2) it has to be at least 0.40 seconds
in length.
--
Chris Green