If you are looking to downgrade your subscription to Aisle Premium or Aisle Plus, follow the guide below.
Open the App Store > tap on Profile at the top right > Subscriptions > tap on Aisle > See All Plans > select the subscription you want to downgrade to.
Changes made to your subscription will reflect after your current subscription expires. You will be billed and charged as per the newly selected subscription plan.
For more information or help regarding the billing process, you can refer to Apple Support.
Google Play currently doesn't support downgrading subscriptions. However, you can cancel your current subscription or wait until it expires, and then resubscribe with your preferred plan.
For more information or help regarding the billing process, you can refer to Google Play Help.