Let him go a few days then try again, Betta's can go along time without food,
When he gets hungrier he might eat them.
I personally gave up on the pellets as to many of mine didn't want them, Tried the week starving with still no difference, Got tired of having to scoop them out,
But you might have better luck,
Also if he's new and spits them out, It's most likely due to unfamiliarity, He's not use to getting them and wants what is familiar to him,
Just gotta be patient and firm with him at the same time,
Alot here feeds pellets with great success,