Hi Kay,
No worries. These are PHP warnings, not errors. Unlike errors, warnings won’t break your website. They’re just messages aimed at developers to improve their code.
To hide these messages, please try pasting the following code lines in your wp-config.php file, just before the line that says ‘That’s all, stop editing! Happy blogging.’:
// Disable display of errors and warnings
define( 'WP_DEBUG_DISPLAY', false );
@ini_set( 'display_errors', 0 );
After that, try to run the demo import wizard again and things should be back on track.
Hope this helps!
Best regards,