Thêm lệnh sau vào function.php

add_filter( 'get_product_search_form' , 'woo_custom_product_searchform' );

function woo_custom_product_searchform( $form ) {

$form = '<form role="search" method="get" class="searchform" action="' . esc_url( home_url( '/' ) ) . '">

<div class="flex-row relative">

<div class="flex-col search-form-categories">

<select class="search_categories resize-select mb-0" name="product_cat"><option value="">Tất cả</option>

<option value="lop-xe-tai">Lốp xe tải</option>

<option value="phu-tung-xe-tai">Phụ tùng xe tải</option>

<option value="thuong-hieu-lop">Thương hiệu lốp</option>

</select></div>

<div class="flex-col flex-grow">

<label class="screen-reader-text" for="woocommerce-product-search-field-0">Tìm kiếm:</label>

<input type="search" id="woocommerce-product-search-field-0" id="s" class="search-field mb-0" placeholder="' . __( 'Nhập tên sản phẩm...', 'woocommerce' ) . '" value="' . get_search_query() . '" name="s" />

<input type="hidden" name="post_type" value="product" />

</div>

<div class="flex-col">

<button type="submit" value="'. esc_attr__( 'Search', 'woocommerce' ) .'" class="ux-search-submit submit-button secondary button icon mb-0" aria-label="Submit">

<i class="icon-search" ></i></button>

</div>

</div>

<div class="live-search-results text-left z-top"></div>

</form>';

return $form;

}