[Plugin: Simple History] can I make the plugin visible for subscribers or editor?

In the latest version you have 2 filters available
simple_history_show_on_dashboard
and
simple_history_show_as_page

If you know how to work with filters you could use these filters to show the history for a specific user. In the current version the user must have edit_pages capability, but this will be possibly to also change with filters in an upcoming update.

The page is only visible to editors and admins. What if I want to show it to my subscriber as well?

Try this in your functions.php-file

add_filter("simple_history_view_history_capability", function() {
    return "edit_posts";
});