how to write for loop to write in my data set if there is a signal

Your question is not very clear. But with the little understnading I got from the question, I guess you want to replace "0" with "1" using a for loop.

Find below a sample code for the same :

A = [0 0; 2 3]; %sample matrix
[r,c]=size(A); %obtaining the number of rows and columns of the matrix
for i=1:r %Iterating through all rows of matrix A
    for j=1:c %Iterating through all columns of matrix A
        if A(i,j) == 0 %Checking if the element in matrix A has value 0
            A(i,j) = 1; %Setting the value to 1
        end
    end
end
disp(A)
     1     1
     2     3

If you want to do this change for 99 different data sets, then you can convert and save this code to a function as follows:

function replacingZero(input_dataset)
[r,c]=size(input_dataset); %obtaining the number of rows and columns of the dataset
for i=1:r %Iterating through all rows of dataset
    for j=1:c %Iterating through all columns of dataset
        if input_dataset(i,j) == 0 %Checking if the element in dataset has value 0
            input_dataset(i,j) = 1; %Setting the value to 1
        end
    end
end
end