zammad/app/frontend/shared/entities/ticket/graphql/mutations/customerUpdate.graphql

mutation ticketCustomerUpdate(
  $ticketId: ID!
  $input: TicketCustomerUpdateInput!
) {
  ticketCustomerUpdate(ticketId: $ticketId, input: $input) {
    ticket {
      ...ticketAttributes
    }
    errors {
      ...errors
    }
  }
}