1. Go to a page on Walmart with a product which you want to sell and see its Page Source. It may look different on different browsers and computers, but you should be able to right click on a page, to see a drop down menu and then select View Page Source. make sure to do not click on an image when doing it, try to click somewhere in a spot on the page where there is no text or any other element.
2. This will open a page with a website's source code. Click CTRL+F (or Command+F on Mac) and search for a word "UPC" to identify a UPC code for a product:
3. Edit your product on GeekSeller, and insert the new UPC code. Then scroll down and click on:
4. In the section Additional Product Attributes, add attribute product_id_override with a value TRUE
5. Click Save and Export to Walmart then go to Feed Status section to make sure the submission was successful.
6. Go back to edit a product, delete the product_id_override attribute (you don't want to send it every time you update SKU) and click Save without Exporting to Wlmart, to just make this change in GeekSeller database.