You can see the initial post here :
office js - How to change the "ReplyRecipients" in Outlook web Addin? - Stack Overflow
Before in the old Addin format we have the ReplyRecipients collection and we could add / change the "reply to" email address.
Now in the new Api the "From" object is read only and we could not change anything (Office.From interface - Office Add-ins | Microsoft Learn).