Warning cannot modify header info

Hi guys i just watched the tutorials and have installed as instructed
Im trying to get the bbc rss feed http://feeds.bbci.co.uk/news/rss.xml?edition=int
But i keep getting this message

Warning: Cannot modify header information – headers already sent by (output started at /homepages/28/d468471118/htdocs/app468471131/wp-admin/includes/template.php:1877) in /homepages/28/d468471118/htdocs/app468471131/wp-content/plugins/rss-post-importer/app/classes/import/class-rss-pi-engine.php on line 652

Any ideas for a newbie?!?

https://wordpress.org/plugins/rss-post-importer/