How to add tax_query to $args with concatenation

Try this…

<?php
if ( $value[ 'priceRange' ] == 0 && $value[ 'tags' ] == 0 && !$value[ 'type' ] ) {
    if ( !$value[ 'priceRange' ] ) {
        $value[ 'priceRange' ] = array( 0, 1000000 );
    }

    $args = array(
        'post_type' => 'product',
        'posts_per_page' => -1,
    );
}


if ( $value[ 'priceRange' ] == 0 && $value[ 'tags' ] != 0 && !$value[ 'type' ] ) {

    $args['tax_query'] = array(
        'relation' => 'OR',
          array(
            'taxonomy' => 'product_tag',
            'field' => 'slug',
            'terms' => $value[ 'tags' ],
          ),
          array(
            'taxonomy' => 'product_cat',
            'field' => 'slug',
            'terms' => $value[ 'tags' ],
          ),
          array(
            'taxonomy' => 'pa_branding',
            'field' => 'slug',
            'terms' => $value[ 'tags' ],
          ),
    );

}
?>