There may be several reasons why a dog does not want to eat new kibble: the size may be unsuitable, it may dislike the flavour or texture, it may be unwell or have dental pain.
So how can you help a fussy dog accept new kibble? Make the change gradually, keep its feeding routine, allow time to adjust, add a little oil or broth, and choose kibble with a flavour it enjoys. Dogs have clear taste preferences. A new flavour, a different smell or an unfamiliar texture may be enough to make them refuse the bowl. This is not necessarily fussiness: the dog is simply expressing its preferences.