Both are in Settings → Data:
- Clear security history: Clear the security history? Messages, senders and rules are kept.
- Clear quarantine: moves every quarantined and blocked message to the trash; they're deleted for good after 30 days.
Clearing doesn't change your rules, trusted or blocked senders, or settings. To keep a copy first, use Export everything.
To delete only some quarantined messages, select them in Quarantine (long-press) and tap Delete.