Thanks all. I got a hold of someone from the 1-800 number after numerous tries. This was on a Friday around 3PM PST. The agent split the ticket I wanted to cancel into a separate reservation. Then I submitted a refund request for the ticket I wanted to cancel (the agent claimed submitting a refund request would also cancel the ticket). I didn't have to cancel the whole reservation and rebook the tickets. But if you're in a time crunch trying to meet the 24-hour free cancelation window and cannot get a hold of EVA Air, I would just cancel the whole booking online and rebook if possible. I hope this helps anyone reading this in the future.