New computers don't need windows reinstalled like in days past since Windows 10 has new Recovery/resetting Options available. Reinstalling windows is not needed or recommended nowadays. Returning to Factory Settings would be the best thing. Go to Dell Support site & enter the tag or model. There is a Download Recovery Image on the drivers and download page under Operating System.  Use the Support link at the top of this page. There is also a link to My Dell Downloads for purchased software and some Dell installed programs.
I just finished setting up this laptop for my sister. I reinstalled windows to so that I could start from scratch, but I realized that I lost the pre-installed software from Dell. Can that software be downloaded from the Dell website?
Retaining the Dell software