I am on this service, but I have the Hub 4 in modem only mode.
I did a self-install. It just required a call to a specified number to get your modem registered and active.
If you are using your Hub 4 in router mode there is little you have to do any different than when you used Hub 3.
Be aware that although your modem will be configured for 1.2Gb the Ethernet ports are only 1Gb, so don't expect to get over 1Gb. Allowing for overheads, you may get very slightly less, assuming you have at least CAT 5e Ethernet cables and 1Gb network cards and switches. However, if you do a speed test using Samknows real speed test you will get a true measure of broadband available, but realistically you only access all of that via multiple devices using a total of up to 1.2Gb. The WiFi is apparently capable of 1.3 Gb on the 5GHz. I cannot confirm what you might get if you have devices capable of accessing this.
https://samknows.com/realspeed/
If you are using modem mode, the conversion from router mode is the same process as in Hub 3. In my experience, it took more than one attempt to get my router to pick up the connection. Be very aware that if your router has a WAN to LAN throughput of less than 1Gb then you won't get close to that speed. Most routers have a WAN to LAN throughput of less than 700Mb! Here's a list of routers with higher throughputs.
https://www.smallnetbuilder.com/old-.../74-wan-to-lan My GT-AX11000 is not on the list, but it has an appropriate throughput. I max at 948Mb via ethernet. My upstream is usually 52Mb. None of my WiFi devices, even those with WiFi 6, has managed any higher than 950Mb even though the AX11000 dishes out over 1Gb WiFi.
Having said all this, my connection has been pretty reliable, but not as consistent as I used to get on the 350Mb and 500Mb services. On a few occasions I have had to reboot the modem because of sluggish speeds below 500Mb. This usually does the trick.