Assuming you have read the data from the file into some sort of collection say List, where EmpData is your object here is what I would do (in almost pseudocode):
List<empdata> emps = ParseExcelData();
foreach(EmpData emp in emps)
if (GetEmpDataFromDatabaseById(emp.Emp_ID) == null )
You would have to write your own ParseExcelData, GetEmpDataFromDatabaseById and SaveEmpData methods.
Hope this helps.