If you want to increase the quantity you purchase during Amazon flash sales, you can follow the steps below:

1. First, make sure you have successfully joined the queue for a flash sales event and the flash sales price and remaining quantity of the product have been displayed.

2. Then, find the "Add to Cart" button or a similar option and click it. This will open your shopping cart page.

3. On the shopping cart page, find the product you want to purchase and click the "Change Quantity" or "+" button. This will allow you to increase the quantity you purchase.

4. You can complete the change by entering the new purchase quantity and then click "Confirm" or "Apply".

5. If your purchase quantity meets the event rules and there is sufficient inventory, your purchase request will be submitted and wait for the system to process. If the purchase is successful, you will receive an order confirmation and a notification of the product shipment.

Please note that different flash sales events may have different rules and restrictions, so please be sure to read the event rules and requirements carefully before participating in the event.