When you have the client still open, you can press ctrl+z to restore them individually. However, if you've already closed you client, there is no way to restore them reself. The only thing you can restore yourself is an entire playlist, which can be done here.
So unfortunately, as a user, you only have the option to restore entire playlists. If you want specific songs to be restored, you'll have to get in touch with the staff. This can be done through a online contact form.
If you get an automated email reply back directing you to the community or help pages, you need to reply directly to that email (even if its from no-reply) and one of the customer services agents will get back to you as soon as possible.