Hello, need some help with the formula below.

I need the index match to look and pull a value from different spreadsheet, however, if it comes back as error (no match), i want it to pull in value from a different cell (S2) - if S2 is blank again, I want the formula to display a text error "No Rep Assigned". Here is how far I got.

=IFERROR(INDEX('SFDC Data.xlsx'!$A:$A, (MATCH(A2, 'SFDC Data.xlsx'!$E:$E,0))),"")