How do I import/update accounts but not the name?

How do I import/update accounts but not the name?

I'm trying to move thousands of accounts from Salesforce into Zoho, but because the SF file is so massive I have to do it in phases.  What I did first was import 2 million accounts with the Name, DUNS (custom unique field), address, owner, and Salesforce Record ID (custom unique field).

That all worked, but now I need to add more details, so the Salesforce Record ID is the primary key, so my new report only has that, plus 10 other custom fields.  However I can't import it as it says Account Name is mandatory, even though I'm just updating existing records using the Salesforce Record ID as the unique key to find duplicates.  I don't want the account names updated, as most these accounts are already in Zoho and under different names from SF, so if I import it's going to overwrite all our account names.  It also doesn't let me make account name not a required field, what do I do?  The future reports won't have account name, only SF ID as otherwise the files are too big since I'm working with 2 million records, so exporting another report that includes account name again makes the file too big for Excel.