How do I mass modify items?

How do I mass modify items?

I want to change the taxes on all items at one time.  how do I do this without going into each item one at a time via the web browser?

I tried exporting the items to a csv.  I made the required edits in exel.  Saved the sheet back to a csv.  But when I attempted to import the items back into zoho invoice, I was unable to do so because there were already items with those names.

please help.

thank you.