How to use App designer when I have several code segments in different files?

So I have 6 matlab files in the same folder that are used when i want to calculate my output. I am trying to create an app that is connected to those files that I have written.

I watched app desginer videos online, but they always just defined a simple function as a callback for a button.

Can I somehow link he app that I want to design to my files? Is there a way to include them in the app code without copying everything in there?

SO lets say I can just call a function when I want to set up a callback for a button ?

so that i dont have to set up variables again and copy in everything from my code..

Tank you