On the 'Support' page you will find the heading Chats. Here you can see all the conversations you currently have open in NiceDay. Click on a chat to open it. You can see the chat history, or write a new message.
To send a new message, tap on 'type here'.
Are you not yet connected with your professional and not appearing as a conversation in the app on the support page? You can read this article to learn how to connect with your professional!