Have a look at your component browser in the app designer, and you'll see app.Tab1 or something similar (as shown above).
Click on app.Tab1 and you will get a list of the Tab's properties - one of those properties is Title. You can modify this property in code-view by:
app.Tab1.Title = strrep(theValueFromExcel,'%',''); % I just use strrep to remove the '%' symbol.
I recommend making a Startup function to set that property, which runs automatically when you open the app. So, you can place that line of code inside the StartupFcn to set the tab name when the app is instantiated. Just make sure that theValueFromExcel is available before your call the the above code snippet.
To create a StartupFcn, navigate to the component browser, right click the top of the tree (i.e. app1 or whatever your app is called) and go to >> CallBacks >> Add StartupFcn callback.
Regarding your concern on the '%' symbol, if you load that into a variable (e.g. theValueFromExcel, in the above code snippet) it will not cause any code to be skipped.
If you can manage this, I would say you're doing quite well for someone who's never used Matlab before.
