Before you run a data conversion batch job to convert a record to a person account, you must set the default record type for person accounts if the record type is enabled. The data conversion job uses the matching settings defined for the default record type if the matching settings are not available for a record type and the object class to which the record type belongs.
You can set the default record type for person accounts in the Edit Record Type Settings page that you can open from the Record Type Settings section of the profile detail page. You can also explicitly set the default record type for person accounts in the Salesforce Developer Console.
The default record type that you explicitly set takes precedence over the default record type that you set in the Edit Record Type Settings page. When you change the default record type in the Edit Record Type Settings page, ensure that you explicitly update or reset the default record type.