Assistance case inside customer incident ticket

[MV]

Hi,

How have you solved in Jira cloud following scenario:
Customer will send ticket Jira service desk and the technician needs assistance to solve it from outside provider. So they need to contact the outside people via email in order to investigate the ticket.
This communication should stay internal and not be shown to customer itself. And we wanna keep the communication in Jira, and not in some email chain.

Is there a tool to add "assistance case private email" to the ticket? Or can this somehow be handled via Parent - child ticket scenario? And how that parent-child would work in the jira service desk?

Thanks