In the app: open ReelGrab → Settings → Delete account and confirm. Your account, list, grab history and connected-service tokens are deleted immediately; copies in backups are removed within 30 days.
Without the app: email support@reelgrabapp.com from the address you signed in with, and we'll delete your account within 30 days.
Lists already synced to IMDb, Letterboxd, Trakt or TMDB live in your accounts there; delete them on those sites if you want them gone too.