This filter modifies the feed title. Copy the code in the functions.php of the theme and replace the placeholder NEW_TITLE with the desired title for the feed.

wp_modify_bloginfo.php

<?php

function mn_modify_bloginfo($content, $feedelementname) {
	
	Switch ($feedelementname) {
		case 'name' : // Feed title
			return "NEW_TITLE";
		break;
		default :
			return $content;
		break;
	}
}
add_filter('bloginfo_rss', 'mn_modify_bloginfo', 10, 2);

?>