I've used my own custom plugin for custom functions and I'm trying to change the default WordPress avatar to my own custom avatar.

My plugin name is "ACh-Toolkit".

I used the following functions but none worked!

function ach_avatar( $avatar_defaults ) {
    $avatar = get_option('avatar_default');
    $new_avatar_url = plugins_url() . '/ACh-Toolkit/images/avatar.png';
    if( $avatar != $new_avatar_url )
    {
        update_option( 'avatar_default', $new_avatar_url );
    }
    $avatar_defaults[ $new_avatar_url ] = 'ACh Avatar';
    return $avatar_defaults;
}
add_filter( 'avatar_defaults', 'ach_avatar' );

function ach_gravatar ($avatar_defaults) {
    $myavatar = get_home_url() . plugin_dir_url( __FILE__ ). "images/avatar.png";
    $avatar_defaults[$myavatar] = "ACh Avatar";
    return $avatar_defaults;
}
add_filter( 'avatar_defaults', 'ach_gravatar' );

function ach_gravatar ($avatar_defaults) {
        $myavatar = home_url() . '/wp-content/plugins/ACh-Toolkit/images/avatar.png';
        $avatar_defaults[$myavatar] = "ACh Avatar";
    return $avatar_defaults;
}
add_filter( 'avatar_defaults', 'ach_gravatar' );

Please help me to solve this problem. Thanks