The plugin does not create those pages – they are done manually, so if you deleted them, you can recreate them manually.
Before you do that, I would look to see if they are in your trash. If they are pages, look in Pages > All Pages, looking at the top for “All | Published | Drafts | Trash” – click the “trash” link and see if they are in there, in which case you can just restore them.
Otherwise, you can just create your new pages an apply the [wpmem_form login] and [wpmem_form register] shortcodes.
For more info, see:
* https://rocketgeek.com/plugins/wp-members/docs/plugin-settings/options/#pages
-and/or-
* https://rocketgeek.com/plugins/wp-members/docs/shortcodes/form/#login
