Hi Ehtisham,
the more specifc the question, the more specific the advice we can give.
Keep in mind that variables are local to a workspace. Thus, the variable Timespan you define in line 17 cannot be used outside of that function. Use properties to share data within an app, see https://www.mathworks.com/help/releases/R2023a/matlab/creating_guis/share-data-across-callbacks-in-app-designer.html.
The intention of line 22 is just not clear to me.
To get started with App Designer, I recommend taking the free App Building Onramp or the full one-day training Building Interactive Applications in MATLAB.
Best wishes,
Harald
