Well, that seems clear. You are asking to import a file that is not in your current directory and is not on your MATLAB path.
If you used something like uigetfile() to have the user select a file, or if you used dir() on a directory to find the file names, you probably forgot to add the directory name into the file name. For example,
[basename, filepath] = uigetfile('*.csv', 'Select a dataset');
if isnumeric(filename);
uiwait(msgbox('User cancelled'));
return
end
filename = fullfile(filepath, basename);
data = csvread(filename);
