By adding this bit of HTML before your Event/Ticket information:
{% for ticket in TRANSACTION.TICKETS | selectattr("TRANSACTION_TYPE", "equalto", "SALE") %}
You just have to make sure the close the loop with an {% endfor %} Merge Tag.
You may want to include this in the templates that you're using for Exchanges.
Here's an example whereby you'd only want the customer to see the Performance Date/Time for their new tickets, not the old tickets they exchanged:
{% for ticket in TRANSACTION.TICKETS | selectattr("TRANSACTION_TYPE", "equalto", "SALE") %}
{{ticket.PERFORMANCE_START_TIME.strftime('%I:%M %p')}} ON {{ ticket.PERFORMANCE_START_DATE.strftime('%a %d%b') }}
{% endfor %}