T = readtable('filename.csv'); % read the file as table
T = fillmissing(T,'previous'); % fill NaNs with previous values
[r,c] = find(isnan(T{:,:})); % check remaining NaN present as a first value in the columns
if(~(isempty(r) && isempty(c)))
T(r,c) = {0}; % fIll with zeros
end
writetable(T,'filename.csv'); % write the table to file
