In your example, "characters ('0','1','2','3','4','5','6')" it looks like the labels might be a cell array of strings. For example
c = {'1','2','3','4'};
If that's the case, you can use
d = str2double(c);
Here's the conversion if the labels are a single string of numbers.
% single string of numbers
c = '1 2 3 4 5';
d = str2double(strsplit(c));