The perfect place to talk about the task before it is assigned is the public comments section on the task page.

Anyone can ask questions, request further information, and reply to each other by posting comments.  In addition, everyone on the platform can view a comment after posting it.

Do not disclose private information or contact details in any of the website's public areas (including comments, attachments, and profiles). The Community Standards that have been implemented to ensure member safety and privacy and prevent spam prohibit sharing this kind of information.

After the assigned task, you are free to communicate securely with the Helper and exchange sensitive information as needed.