When you import a list with unknown headers, you can create field aliases to make it easier. You can also edit those aliases in field management. Check it out.
Admin Permissions Required
Under Admin, click Field Management.
Find and select the field you want to add an alias to.
In the Field Actions drop-down, click Edit Import Aliases.
Enter an Alias and click Save.
Click Add Another and enter more aliases if you need them.
Look at that! Now if you import a spreadsheet with a column named “DOB,” Marketo will automatically recognize it as “Date of Birth” and import the data into the correct field.