Is there an app that I can use on my iPhone SE that will scan WalMart barcodes?

Walmart provides their app to scan barcodes for the items in the store. You can also use Walmart Pay using the app. Be careful though, the app provides constant pop ups to get you to join their Walmart+ subscription service and if you do not pay attention to what you are tapping, you will be charged for it.

To scan a barcode with your iPhone, you'll need to download an iOS barcode scanner app. There are a large number of paid and free iPhone barcode scanner apps available. Once installed, open the barcode scanner app, click the scan button, and place the barcode in view of your iPhone's camera

Barcode scanning is a feature of the iOS camera (depending on what version of iOS you're running). However, the more important question here is what is your goal? What do you want to do with the information your scanning?