Currently, we do not have the functionality in place for you to add additional text fields for end users submitting Issues in the SDK. While you can add custom fields to your Web Support Portal contact form, the in-app contact form will contain the only name and email fields. However, depending on what additional information you want to collect with this form (device data, user account information, etc.), you may be able to pass it as custom metadata when the user files a new Issue.
To learn more about implementing custom data tracking, see our developer documentation on attaching metadata to conversations in iOS and Android.