Replacing my Xfinity Gateway with a store bought Gateway

Hello,

I purchased a new gateway that is being shipped to me, but I needed some clarification on getting it set up.   I found the installation instructions online, which called for me to attach the coaxial, plugin power, and open the manufacturer App  (SurfBoard) after bootup to configure the modem.  When I read the Xfinity instructions it tells me to attach the coaxial cable, plug it into power, and after bootup open the Xfinity App.   I'm confused and hoping someone can clarify this.  Do I configure the modem with the Surfboard App or instead just use the Xfinity App???   Thank You in advance for any help offered.