You cannot do so directly through Genesys Cloud, as part of that same conversation.
The best way, probably, would be to have the supervisor go into the Performance>Interactions view, find the conversation, and then manually send an email On Behalf of Queue. The supervisor would need to copy/paste the customer's email address from the Interaction view, copy/paste the subject, copy/paste the body of the last email in the conversation. Then write the corrections or whatever in the new email and send it.
https://help.mypurecloud.com/articles/send-outbound-email-behalf-queue/You could also create a custom application that allows someone to send a Reply to an email conversation via the API:
https://developer.mypurecloud.com/api/rest/v2/conversations/#post-api-v2-conversations-emails--conversationId--messagesOr, for someone who has the permissions and ability, they could use the API Explorer to send an email reply to a conversation using that same API function.
------------------------------
George Ganahl GCP (Genesys Cloud), ICCE
Principal Technology Consultant
Genesys
------------------------------