You can downgrade your account to a free plan via the Billing tab in settings:
Downgrading to the free plan limits your search history to the past 90 days. To search your full historical archive, either head to Gmail or upgrade back to a paid plan. To learn more about managing billing and plans, check out our explainer here.
If you need any help with your billing setup or are looking for a refund, reach out to firstname.lastname@example.org.