Check whether the chat is archived in WhatsApp
Restore the chat from an iCloud WhatsApp backup
Reinstall WhatsApp and verify the same phone number
Open WhatsApp and tap Restore Chat History when prompted
Restore from an older iPhone backup if available
Check if the chat exists on another linked device
Ask the other person to resend the conversation or media
Use a third-party iPhone data recovery tool only if you have no backup
Enable WhatsApp iCloud backups to prevent future loss