Your code seems to be all wrong so check it out:
All your "MyValues" are declared as String, not as an array.
In your code, you are indexing them as if they were an array.
You are not checking if the worksheet already exists, you're always adding it (which should be fine if you are creating a new file every time e.Values(0) becomes True):
ExcelPackage.Workbook.Worksheets.Add(MyValues8)
Even when you add it the code afterwards, for the header creation, is not pointing to that worksheet:
ExcelPackage.Workbook.Worksheets(MyValues0).Cells("A1").Value = "Part Serial Number"
ExcelPackage.Workbook.Worksheets(MyValues1).Cells("B1").Value = "Operator Name"
ExcelPackage.Workbook.Worksheets(MyValues25).Cells("C1").Value = "Date / Time Stamp"