[otrs] Help -> Information after merging tickets

Hi ! I want to create an email for the ticket-owner, after a new ticket was merged to an existing ticket. I try to create an event-notification, but I always get an email with information about the new (merged) ticket and not about the existing ticket. :-( I which way can I realise it ? Any help is welcome :-) Thanks in advance . Best regards, Stefanie Krüger