In your case the best solution is 301 redirection.
If you don’t know what was your old permalink then go to Google search console and it will show you all 404 error pages. If you signup to search console right now, then still you can see those errors but after some days.
If you’re using some kind of CMS like Wordpress, Drupal or Joomla, then you will find lot’s of plugin which will help you to setup 301 redirection very easily.
If you’re using Blogger, then it also support 301 redirection (Go to setting > search preference > Edit custom redirects).