Import Leads - Find existing leads based on

Import Leads - Find existing leads based on

I am a new user and testing things out....
I have imported a bunch of leads, then updated my external spreadsheet and now I want to update those leads in ZOHO.

I have exported the data in a CSV (exactly like when I imported the leads) and when I check the box "Update Existing Leads Only" the only option under "Find existing leads based on" is "Lead ID".

According to the help page:
These can be filtered based on record's ID, name or email address, as per the module.

I have confirmed that my Email Address field in the Spreadsheet is EXACTLY like it is in ZOHO.
Any ideas on why I can only key these using Lead ID?

I really need to update existing records by Email Address.

Thanks,
-Owen