@Happydayyy In your save as file did you intend to enclose Completed in quotes because you haven’t and that might cause error if Completed isn’t a name of a variable.
If Completed is variable then check if the variables (AppNumAll, etc) in that activity have a value. you can use the variables panel during debug to check value or log the values before the activity to see what values they have
You have Kill Process inside your Use Excel File. You can’t do that. You’re killing the process that has the Excel file open, so then the Excel variable in the Save Excel File As activity has no value. You don’t need the Kill Process anyway.
I think you are releasing/garbage collecting/killing the Excel Workbook object before this activity. That is why studio is throwing Object reference not set to an instance of an object
Check this and remove that step and you should be fine!
Thanks,
Ashok 