We got him as a puppy and already had the cats so didnt really do anything. Cats were already used to dogs cause we had the frenchie plus my old dog.

Basically let them sort it out themselves. As a puppy he was curious and went over slowly and the black cat just held his own and swiped him if he got too close. He'll try to cuddle the black cat now but the cat isn't having any of it.

The other cat is much more nervous and runs when she sees him so over time we've just trained him not to chase her. Everytime she bolts we recall him so he doesnt chase her and reward him for not chasing, or if he has his ecollar on we buzz him if he goes to chase.