The steps to purchase Wallace’s redemption code on Meituan and place a self-service order are as follows:

1. Open the Meituan App and log in to your account.

2. Enter "Wallace" on the homepage or search bar, and select the city and store where "Wallace" is located.

3. Browse Wallace's menu and select the items you want to purchase.

4. Find and click the "Buy" button at the top of the product page.

5. On the ordering page, choose the dining method that suits you. There are usually two options: "Dine now" and "Dine in advance".

6. From the options visible below, find and select "Redeem Code".

7. Enter the Wallace redemption code you have and click "Confirm".

8. Fill in the delivery address, contact information and other necessary information according to the page guidelines.

9. After completing the payment, you can choose the payment method for settlement.

10. After placing the order successfully, you will receive the order confirmation message, and then wait for delivery from Wallace or go to the store to pick up the food yourself.

Please note that during the actual operation, the interface and steps may change due to updates to the Meituan App. The above is only a general process, and the specific steps are subject to actual operation.