Your post suggests that the wrong input is selected for the TV. (i.e. it's looking for a signal from an aerial, or similar, when it should be taking the output from the Sky box).
Make sure you know which remote is which.
Turn the TV on. (I'm assuming that the Sky box is on by default. If not, make sure that's turned on too).
On the remote control for the TV, look for a 'Source' button. It might be labelled 'Source', 'Src', 'Input' or something similar but it's usually marked by a rounded rectangle with an arrow pointing into it, like this:
https://tinyurl.com/yddnr7l3 . Press that button.
You'll now see a menu offering options such as 'DTV', 'Scart', 'HDMI1'. (The exact labels vary across different TV models). Use the Up and Down buttons to move between those options. The one you want is probably something like 'HDMI1' but it doesn't really matter. Just go through the available options until a picture appears. When it does, press the 'OK' or 'Select' button to confirm the option. (It's often the biggest button on the remote control).
From then on that remote control should only be used to turn the TV set on or off (and possibly to control the volume). Use the other (Sky) remote control to change channels.