Append Records to Existing Data

Append Records to Existing Data

I have a database which includes: SALE DATE, ITEM CODE, END CLIENT.
The END CLIENT field is currently empty.

I have a excel sheet on my PC which lists all ITEM CODEs and who the END CLIENT is.
I attempted to update all records in Zoho Reports with the END CLIENT name, hoping it would match the ITEM CODE.
Unfortunately, it simply added all the records at the end.

There are duplicates of ITEM CODE in my database because they are purchased multiple times and have different SALE DATEs.

How can I map ITEM CODE as a lookup so that END CLIENT is added to each record where ITEM CODE matches itself?