Hi Lai Ngee,
Yael from WorldNomads.com here.
You can't change sports & activities listed on your insurance certificate after you have purchased. However, I would suggest that you contact our Customer Service team: https://pp.worldnomads.com/contact-us - as they can advise what you need to do so that you can make sure you have the right coverage when you travel.
Happy travels! 6 months ago