Managing or canceling your subscription — this is handled entirely through Apple. Go to Settings on your device → your name → Subscriptions.
Restoring a purchase on a new device — open Calibrate, go to any Premium screen, and tap "Restore purchases."
How accurate is AI-estimated nutrition? — see the in-app Help section (Profile → Help) for a full breakdown of how barcode scans, database search, label scans, and AI estimates compare.