Log in to your account on the NordVPN website, then go to My Account, click on Payments and at the bottom you will see Cancel Subscription, click on it, select the reason of the cancellation then click on yellow Continue button. Afterwards click yellow Continue button once again, and finally click the yellow Cancel My Subscription button to verify your recurring subscription cancellation.

For subscriptions made through iTunes, please check this Apple support article about iTunes subscription cancellation: https://support.apple.com/en-lamr/HT202039

For subscriptions made on Google Play, you can cancel the subscription by following this guide: https://support.google.com/googleplay/answer/7018481