When adding custom fields to ConvertFlow form elements, you can choose to select from "Intercom fields". This allows you to map contact info entered into the ConvertFlow custom field, into the correct contact custom field in Intercom.

When you create a survey element in ConvertFlow, click on the "Map to custom field" dropdown to the right in the builder panel, and you can select from your Intercom custom fields.

On your website's Integrations page, when you have Intercom connected, you'll see a "Fields" mapping interface, that allows you to map ConvertFlow's preset contact fields to Intercom custom fields.
​

This is useful for mapping contact info added to ConvertFlow's preset fields through ConvertFlow's forms, that isn't already mapped to fixed fields in Intercom. For example, "first name" and "email address" are already mapped to Intercom for you.
​

To use this, select the Intercom custom field respective to the ConvertFlow field, and then click "Save".