You can cancel your Soco subscription any time from the Soco app, and you finish the cancellation in your Apple subscription settings. Soco can't cancel it for you, because Apple handles all subscription billing.
Cancel your Soco subscription from the app
To cancel your Soco subscription:
Open the Soco app.
Tap the account icon in the top right.
Under Help, tap Manage subscription. Your Apple subscription settings open.
Follow Apple's prompts to cancel Soco.
Apple's subscription screen then shows Soco as expiring on a date instead of renewing. That means it's cancelled.
Cancel your Soco subscription if you can't open the app
You can cancel your Soco subscription from your Apple Account without the Soco app. Apple's own guide covers every device: If you want to cancel a subscription from Apple. The confirmation is the same: Soco shows as expiring on a date instead of renewing.
What happens after you cancel
After you cancel your Soco subscription you keep Pro until the end of the period you've already paid for, and you aren't charged again. Deleting the Soco app or deleting your Soco account does not cancel the subscription; only cancelling in your Apple subscription settings does.
Next steps
Your next question is probably one of these: