Clearing a chat allows you to clear all messages inside a chat.
Clear an individual or group chat
In the Chats tab, open the individual or group chat you want to clear.
Tap More in the upper right corner > Clear chat.
Tap Clear chat.
Clear all chats at once
In the Chats tab, tap Settings > Chats > Clear 小hat History.
Tap Clear 小hat History
Please note, that after deleting all chat history, you will not be able to revert it.