How can I create an 'Import button' - that imports excel files - for my GUI using appdesigner?

I'm currently working on a gui, wherein one of its features is to have a button that is able to import excel files into the program. I have a push button, and it creates a pop-up menu that stands as a file browser. However, when I run the program and then select a file to open it with, it doesn't work. :( The only working portion of my code for the import button is this:

app.Import.Enable = 'on';
            [FileName,PathName] = uigetfile({'*.xlsx'},'File Selector');

I was really hoping someone could help me with this :( Thank you!