Walmart doesn't sell eBooks directly, they forward you to a branded version of the Kobo store for eBook sales.
On Kobo login (depending on how you set things up you'll use your Walmart login, a Kobo login, Facebook login or Google login, I'm guessing you used Walmart credentials). Then click on the upper right where it says "My Account" and select My Books from the drop down. Any purchased books should be listed there.
To download an ePub copy (using Adobe Digital Editions for DRM'd books) click on the three dots (...) under the cover (right side) and select Download. For non-DRM'd content the ePub can be downloaded directly to a computer, for DRM'd content ADE is required (see below). The other way to read Kobo content is to download it directly to a Kobo device or app that's logged in to the relevant account.
How to download DRM'd content using Adobe Digital Editions...
https://www.kobo.com/help/en-US/arti...gital-editions
Most of us on MobileRead will usually recommend using ADE 2.0.1
https://www.adobe.com/support/digita...downloads.html
As Ducks mentions to convert for use on Kindle the DRM will have to go (assuming it was DRM'd) and Apprentice Alf's blog can help with that. We aren't allowed to go into details on DRM removal here.