Call custom portfolio in functions.php

//Add to functions.php

//======================================================================
// CALL UP THE CUSTOM PORTFOLIO WITH EXCERPT FILE - custom_portfolio
//======================================================================
function custom_portfolio_excerpt() {
    if ( ! class_exists('ET_Builder_Module') ) {
        return;
    }
    get_template_part( '/custom_portfolio' ); //location of your portfolio module in child theme
    $custom_portfolio = new Custom_ET_Builder_Module_Portfolio();
    remove_shortcode( 'et_pb_portfolio' );
    add_shortcode( 'et_pb_portfolio', array($custom_portfolio, '_shortcode_callback') );
}
add_action( 'et_builder_ready', 'custom_portfolio_excerpt', 9999 );