Replacing old router with new Xfinity gateway and faster speed service - do i need new coaxial cable

I just upgraded my service to higher speed and received in the mail a new xfinity gateway router. I am unable to install like the video instructions tell me because my coaxial cable access is going through the wall to the exterior of my house, down a floor, around the corner and hooking into a cable splitter outside. I can't seem to find any way to chat or talk to an agent for help. It doesn't look like anyone can come to install due to Covid-19. Can I use my existing coaxial cable coming in from the outside? Or will that not allow for the faster speed I just upgraded and am now paying for on my account? Someone help me please as I cannot work from home effectively without better internet service.