Open WhatsApp on your iPhone
Tap Settings
Tap Chats
Tap Chat Backup if you want to manage or delete backups in iCloud
Go back to Settings
Tap Storage and Data
Tap Manage Storage
Select a chat or media type
Tap Delete or Delete All
To delete a specific chat, go to Chats
Swipe left on the chat
Tap More
Tap Delete Chat
To delete all WhatsApp chats, go to Settings
Tap Chats
Tap Clear All Chats or Delete All Chats
Confirm the action
To delete WhatsApp app data completely, press and hold the WhatsApp app icon
Tap Remove App
Tap Delete App
Confirm deletion
To remove iCloud WhatsApp backup, open Settings on iPhone
Tap your Apple ID
Tap iCloud
Tap Manage Account Storage
Tap WhatsApp Messenger
Tap Delete Data