To purchase Amazon Commercial Liability Insurance, you can follow the steps below:

1. Log in to Amazon Merchant Center and enter your seller account.

2. Find and select "Services" or similar options in the menu.

3. In the service options, find and select the insurance-related service. It may appear as "Commercial Liability Insurance" or similar names, and the specific name may vary depending on your region.

4. Click the relevant service option and you will be directed to the insurance purchase page.

5. On the insurance purchase page, you will be asked to fill in some details, such as your business information, product type, location, etc. Make sure to fill in accurate information to get an accurate insurance quote.

6. According to the instructions on the page, select the relevant insurance options, coverage and insurance period. You can decide what level of insurance coverage to purchase.

7. After confirming the purchase of the relevant insurance, you will be asked to pay the corresponding insurance fee. You can choose a suitable payment method, such as credit card, debit card, etc.

8. After completing the payment, you will receive insurance purchase confirmation and relevant documents such as the policy. Please keep these documents in case you need them in the future.

Please note that the above steps may vary depending on your region and changes in Amazon policies. In order to ensure accurate information and operation procedures, it is recommended that you contact Amazon Customer Service directly or visit the help section of Amazon Seller Center for the latest and detailed guidance.