He could just be getting used to his new home since you've only had him for 1 day. I would wait until tomorrow to feed your betta. He is probably just adjusting to his new home. How many gallons is your tank? And is it heated? Those could also be the problem. Hope this helps!
R.I.P I will never forget you Alexander. You brightened my life
♥Alexander ♥- Maroon VT 11/14/10
I miss you every single day. You were more than just a pet to me. I love you forever and always. I hope you always know that I would have done anything to save you.