Welcome to SaleHoo!
If it is not a required field (as most are optional) you can just leave it blank.
But do note that there are suppliers who only sell to registered resellers or those who have an actual business online or a brick and mortar store. So in this case, even if you make up a a company name in the end you will still be required to provide a resellers or tax ID.
Hope this helps...Cheers :)