Finding a large hidden signal inside another signal

I have 39 files named 'rudenko_01.wav'......'rudenko_39.wav'. I have a variable named findme which is an audio segment present in one of the 39 files and also I have to find the index where the segment is. I am told to use correlation and fft to find those signals. This is what I have done.

files = dir('D:\Signal Processing\HW7\*.wav');
audio = cell(1,39);
for k = 1:39
audio{k} = audioread(files(k).name);
end
for i=1:39
    Corr{i}=conv(audio{i},fliplr(findme));
    M{i}=max(Corr{i})
end

I have done the correlation part. I am getting some answers but I'm not sure how to use the results of 'M' to find the file. Can you please help?

This is the question

'Utilize the capabilities of correlation and speed of the FFT to determine which music le

contains your unique audio segment findme. Note that even when using the fft function,

your script may take a few minutes to fully execute. Identify the le containing your music

segment and the index which the segment is found in the music.'