Hello
If you didn't purchase the license from Microsoft, and the computer is pre-built and came with license, your license is not necessarily digital. In this case, builders typically use OEM-NSLP license, and if the builder is compliant, they must apply the sticker with the license key somewhere on the computer, or at least give you the box that still has the sticker intact.
Look around to see if you can see the sticker somewhere on the computer. That's what you need, the key.
If you never received the key from the builder or cannot find it, you need to reach out to the builder because it is yours to keep and you need it for the future too.