Steps:

1. Open your mobile phone, find Pinduoduo app, and click Enter.

2. After entering, select "Personal Center" in the bottom menu bar, and select all orders in the personal center.

3. After entering the page, click "Invoice Assistant" in the upper right corner.

4. Find the invoice to be written off, click and select the order to be written off.

5. After the application is successful, click Save Invoice.

Invoice refers to the business vouchers issued and collected by all units and individuals in buying and selling goods, providing or receiving services and engaging in other business activities. It is the original basis of accounting, and it is also an important basis for law enforcement inspection by audit institutions and tax authorities.