There aren't many reasons to switch a subscription assigned to a player. However, if you accidently cancelled your subscription currently there is no way to undue this change. It will be required to purchase a new subscription and swap the subscription before the original expires. Also, you may want to save some money by migrating from a Monthly to a Yearly subscription.
This is the process for changing subscriptions: https://youtu.be/xcstEpLxBIw
Note: In the case of migrating from a monthly to a yearly subscription, please be sure to cancel any unwanted monthly subscriptions.