When you begin a free sample migration with Import2, you will have the following options to migrate your custom fields:
Import2 can automatically create and populate the custom fields for you.
This will be dependent on whether your new app supports this feature. If it is available, you will see this option during the sample migration setup prompt:
You can choose to add and/or change mappings yourself.
After your sample is complete, you can navigate to the Customizations tab of your migration page and adjust the mappings as needed. This is available both if you opted to have us auto-create your custom fields, or not.
You can see all mappings on this page, including both standard and custom fields:
And you can add or change mappings as needed:
When you are finished adjusting your mappings, you will need to go back to your Summary tab, and click "Restart Sample Migration" to apply your changes in a new sample.