@Manisha541 are they always going to be in the same order? Meaning row 1 from excel1 needs to be subtracted from row 1 in excel2, etc.
If that is the case, you can achieve this with a single for each row loop. I’m assuming you want the output in a new column called ‘Output’ in the excel sheet containing inventory.
1. Read Range activity for both excel files. Save as dt1 (excel with order qty) and dt2 (excel with inventory)
2. Add Data Column to dt2 of type integer named "Output"
3. For each row in dt1 (save the index output property of this activity to variable called rowIndex)
a. Assign dt2.rows(rowindex).item("Output") = CInt(dt2.rows(rowindex).item("Inventory")) - CInt(row.item("Order Qty"))
4. Write range activity to write dt2 back to excel sheet