Sometimes orders are cancelled by mistake.
Perhaps your buyer emailed to cancel their booking, then emailed again to say they wanted the ticket, but their email was lost. Or, they cancelled a booking by mistake themselves, via Self-serve.
If you want to reinstate a cancelled order you can either:
Rebook the ticket for your buyer. How to place a manual order.
Or;
Ask your buyer to place a new order from your event page or website.