I just got the Galaxy S8 from best buy, Verizon has been our carrier thru many galaxy.. I gave no HD calling or Video calling. There is not even an advanced calling section in settings. The VolTE is on, but it does not say that it allows HD or video calling.
I got my phone directly from Verizon and the default dialer has this built in. It is called "Samsung Call." If you have some other dialer since you got it from Best Buy I'm not sure what dialer you have. Under call settings with the regular dialer there is a "Video Calling" on/off toggle. If this is on then you can select a contact and initiate an HD video call but I always use it in the middle of a call after asking the other party if they want to switch to video mode and it works very well, probably even better than Skype if both parties are on the Verizon network. If you don't have the "Samsung Call" app then try searching the Samsung Galaxy Apps store for it.