ImportWP Pro gives you the ability to import from both XML and CSV files into custom fields for WordPress posts, pages, custom post types, and users.
Click on the add button on the right hand side of the custom field meta box (+) to add a new custom field record, within this record select the custom field you want to add, for example if you are using Yoast SEO plugin you can choose to populate fields such as focus keyword, seo title, and seo meta description.
If you cant find the custom field you are looking for, you can check the Enable text fieldcheckbox that will allow you to manually type the custom field key you want to import to.
All that is left to do is click on the select button under the Value column to load up a modal allowing you to select which data from either the csv or xml file that you want to populate with.
An example of populated custom fields importer box with some selections: