Depends what you mean.
Virgin Media don't need to so anything if you are talking about Freeview, TV through your aerial. If you mean TV provided by Virgin Media via the cable from you street I'll cover that later.
Your Internet-enabled TV will have an Ethernet port and also probably WiFi. Choose which you want to use.
For the former you run an Ethernet cable from your TV to a spare port on your broadband router.
For the latter you go into the TV's settings menu, select the Set-up procedure for it and enter your WiFi details like you would with your mobile/tablet/laptop/desktop PC.
Once successfully connected you can choose streaming channels via the Freeview EPG, they are in the channel number range of 260s-270s, or use the Apps built-in to your model of TV, which vary depending on manufacturer and model.
If you meant TV provided by Virgin Media via a cable from your street it depends if you are already a TV customer with them.
If you have Virgin Media TV with a Tivo or V6 box you will have to change the Input/Source on the TV via the remote, as when you are using Cable TV the box is plugged into an HDMI whereas the TV's built-in Internet functionality obviously uses internal components.
If you are not a Virgin Media TV customer and wanted their service, that is the only time you'd need an engineer from them. If you only have broadband from VM and want to use your new TV's built-in functionality, then no engineer is needed. You simply plug one cable from your roof aeriel to your TV for broadcast TV and either setup WiFi or attach an Ethernet cable from your TV to the broadband internet router to allow the features that require the internet to work.
Hopefully this is clear and understandable and I've not confused you further.