Use pellets for food, put it on a table, press your finger against it and it will stick. Then you put your finger just above the water line right in front of your betta so he sees it. Don't touch the surface it may fall off your finger, and wait till your betta eats it. Keep doing that and he will love your finger.

 

I would also put a bloodworm on my finger, dip it in the water and feed him.
He's still new, I wouldn't worry about him, once he starts to make the association between you and food, you'll be surprised.

 

they take a little while to settle in.
The stress of transport, etc.
Theyre known not to eat for the first day or 2, but yeh do what they said and he will
come to love it.
You said your a new owner, so id recommend soaking the pellets in a bit of tank water (least ammount possible) for 5 mins
and they will stick to your finger, and be easier on his stomach.

Oh and always clean your hands when feeding from your finger