Access Settings, then tap on your name and choose iCloud. Toggle off the Calendar option to prevent further spread.
Open the Calendar app, select the suspicious event, and tap "Delete Event" to remove it from your calendar.
Navigate to Settings > Passwords & Accounts > iCloud, turn off Calendars, then go to Settings > Calendar > Accounts and delete all accounts.
In Settings, tap on Calendar, then Default Calendar, and select a different calendar. Return to the original calendar to reset it.
Ensure your iPhone has the latest iOS version installed to patch any vulnerabilities that might have been exploited by the virus.
Install reputable antivirus software from the App Store and perform a scan to detect and remove any remaining malware.
Activate two-factor authentication for your Apple ID to enhance security and prevent future unauthorized access.