y = readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1013745/Book1.xlsx');
L = numel(y);
x = linspace(0, L-1, L);
figure
plot(x, y)
grid
yf = smoothdata(y, 'sgolay', fix(L/25));
figure
plot(x, yf)
grid
Experiment with the window size (third argument in smoothdata) to get the result you want.
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