How to change a "More" on right sidebar?

You can either modify the text in the theme file sidebar-2.php or use this function:

/* --------- change text -------- */
add_filter( 'gettext', 'my_custom_text', 20, 3 );
function my_custom_text( $translated_text, $text, $domain ) {
    switch ( $translated_text ) {
        case 'More' :
            $translated_text = __( 'Right Sidebar', 'hueman' );
            break;
    }
    return $translated_text;
}

In either case you’ll need a child theme:
1. In Theme Options click the Help tab in the upper righthand corner.
2. One of the options in the list is to download a sample child theme. This downloads the theme zip file to your local computer.
3. Install the new theme in your Admin panel by selecting Add New > Upload Theme > Choose File, then select the zip file you downloaded.
4. Activate the child theme.
You’ll now have a pre-configured child theme with a style.css file and functions.php file to which you can add customizations.

Thank you bdbrown. I access sidebar-2.php and it works!