bbPress.org

Put this in your child theme’s function file – or use https://en-gb.wordpress.org/plugins/code-snippets/

and change ‘new text’ to whatever you want

//This function changes the text wherever it is quoted
function change_translate_text( $translated_text ) {
	if ( $translated_text == 'Create New Topic') {
	$translated_text = 'new text';
	}
	return $translated_text;
}
add_filter( 'gettext', 'change_translate_text', 20 );