You can switch the subscription price or duration in Google Play App on your Device.
To change a prepaid subscription plan:
- Open the Google Play app
.
- Make sure you’re signed in to the correct Google Account.
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Tap "Payments & subscriptions" button, then "Subscriptions" button.
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Tap "Payments & subscriptions" button, then "Subscriptions" button.
- Find and open the Nebula app in a list.
- Tap Manage subscription.
- Select the new plan you want to change to.
- Select a supported payment method.
- Tap Buy or Subscribe.
Here is a guide from Google: https://support.google.com/googleplay/answer/7018481?co=GENIE.Platform%3DAndroid&hl=en#zippy=%2Cchange-between-subscriptions-prepaid-plans