advanced custom fields - Convert number to date format within an array

I have a custom field of deal_date that I need to work into an array. When using directly on a template I can just set the output format directly in the ACF UI. However I obviously cant use get_field within an array, so the output in this scenario is just the number showing up as a string (ex. 20180422) - how can I convert this within the array so that it shows up as a date (ex April 22, 2018).

$posts = get_posts( $args );

        if( $posts ) :
            foreach( $posts as $k => $post ) {
                $source[$k]['ID'] = $post->ID;                                      
                $source[$k]['label'] = array ( $post->post_title, $post->deal_date);                
                $source[$k]['permalink'] = get_permalink( $post->ID );