First, you can complain to the platform's customer service, providing the order number, evidence of the product's quality issues, and details of the seller's delay in handling the issue. The platform usually will intervene and urge the seller to deal with it as soon as possible. If the problem remains unresolved, you can apply for the platform's advance compensation service (supported by some platforms). Meanwhile, keep relevant evidence, such as chat records and product photos. If necessary, you can seek help from consumer associations or take legal action to protect your rights.