Hello, Ahmed
Please watch this video – https://youtu.be/LgzC4iK-j6A You provided a link to a simple product, but you need to select a variable type for this product and configure it – https://woocommerce.com/document/variable-product/
If you have any additional questions or concerns, please do not hesitate to reach out to us. Our support team is always available to assist you.
Kind Regards, 8theme team
