I have accidentally subscribed for 1 TB STORAGE PLAN

Hello there, bharatphullera.

To cancel your iCloud subscription there are a few Knowledge Base articles that offer some great information.

iCloud: Cancel your storage upgrade

If you upgrade or renew your storage but no longer need it, you can cancel. If you cancel your storage plan within 15 days of an upgrade or within 45 days after a yearly payment, you can contact Apple for a full refund. After this period, you can downgrade your storage for the following year.

Note: Partial refunds are available where required by law.

Additionally this article offers some more information as well:

Changes to iCloud storage for current customers - Apple Support

How do I change my plan?

You can use these steps to change to a monthly storage plan at any time from your iPhone, iPad, iPod touch, Mac, or PC. After you change your plan, the annual plan will no longer be available. Learn more about storage upgrade pricing.

If you want to request a refund, you should contact Apple Support within 15 days of the upgrade. Partial refunds are available where required by law.

Thanks for reaching out to Apple Support Communities.

Cheers,

Pedro.