Do you mean deleted by yourself or the administration? If you want to know how to restore posts or comments you've deleted, then unfortunately, there's no way. Once they're deleted, they're gone. There's a chance you can get posts deleted by the admins back but it's unlikely. You can do so by viewing your notifications from the administrators and then telling them you have not violated the Miiverse Code of Conduct. They will eventually tell you if they've declared the post okay or not. Hope I helped!