How can I restore deleted messages?

There is no way to restore deleted messages.

However deleting messages works just on one side your friend still has those messages, unless he has deleted them as well. You can ask your friend to forward them to you. You can forward up to 100 messages at once.

Be careful extensions, apps and sites that promise you to restore your deleted messages are dangerous. There is nothing behind these empty promises but malware that aims to steal your passwords. By using them you risk losing money and access to your page.
Your search for returned no results.
Try using other keywords, e.g.: "delete profile", "create chat".
Check your request for misprints.