Hello Julio, 

Unfortunately, there is no possibility to start the chat with existing contacts from the system. The chat feature enables you to receive requests from external users at the moment. We will raise the idea for R&D team to implement this feature for chats in further releases. 

You can find more detailed information about chats in the Communications - Work with chats Academy article. 

Best regards, 

Olga. 

Olga Avis,

Thanks Olga