I have tried several times importing a list CSV with columns including:
On Import I have chosen Marketo Fields: First Name and Lead Owner First Name
Nothing has allowed the first and last names to display
I have tried so many times with matching and variations of Marketo suggested column names
Job title and email display, but never first and last names
Lead Owner is an SFDC field and is blocked in Marketo. You cannot, nor should not, change it. You cannot "assign" leads in this method.
Suggest you try