You need to create a listbox where the user can click on the files to process. Then in the opening code, load up the listbox with code like this.
% Specify top level folder and file pattern.
topLevelFolder = pwd; % Or whatever you want.
filePattern = fullfile(topLevelFolder, '*.dat')
% Get a list of all files in that folder and within its subfolders.
ds = fileDatastore(filePattern, 'ReadFcn', @readmatrix)
allFileNames = ds.Files
app.Listbox.Text = allFileNames; % Or maybe it's app.Listbox.String -- I don't recall.
Then in your "Go!" button, or however you start your batch process, you need to get the Value of the listbox to determine which items were selected, and get the Text property to get all the file names, then loop over selected indexes getting the current data filename and doing something with it.
