[Plugin: RSS Manager] Some errors

On the website itself I get the following error:

Notice: load_plugin_textdomain was called with an argument that is deprecated since version 2.7 with no alternative available. in /var/www/wordpress/wp-includes/functions.php on line 3553

On the backend in the settings I get the following error:

Notice: Undefined index: rm_submit in /var/www/wordpress/wp-content/plugins/rss-manager/rss_manager_admin.php on line 7

If you could fix this, I will use the plugin. Now it’s not possible ??

https://www.ads-software.com/extend/plugins/rss-manager/