If you are trying to switch from a monthly recurring subscription to an annual subscription, please follow these steps. 
APPLE DEVICE
Below are the step-by-step instructions and included here is a simple screen recording showing the same steps.  

STEPS

  1. Select your Apple settings app
  2. Choose your name (Apple ID) next to your photo
  3. Select Subscriptions
  4. Select Todo Cloud
  5. Select the 1 Year Premium subscription