your fish is new so he needs time to get used to the new enviorment. and he might not eat either (if you havnt already tried) bcuz they usally dont eat for a couple days. so dont worry and give him his needed time.
whats his tank size?
does it have a filter?
did you cycle the tank? (this will not be the problem just curious)
welcome to the forum :D and good luck with your betta