your 6 week old should no longer need to be fed from a bottle and should have been eating on his own by now...and should still be at home with his mom.
I suggest you get "royal canin baby puppy food" add a bit of water, microwave it for about 20 seconds to take the chill off, let it absorbe the water getting a bit soft then add a bit of formula if you like but not necessary...I then mash it up till about 8 weeks then I dont add anything to soften it because their milk teeth are in and need things to chew. I keep them on baby puppy food till they leave my house and send some off with the new owners to use for a bit longer then change to puppy food till at least one year old. I believe the fatter the better the first year!
if that doesnt work go buy jared baby food the chicken sticks and feed your baby that to get him eating on his own, give him pleanty of water too!
Your breeder is irresponsible for sending home a pup that has to be bottle fed let alone this young...Please take him to the vet and make sure he has the ability to eat on his own...perhaps there is a reason she was still feeding him by bottle which wont be good news to you.
he should have not left home until at least one puppy shot and totally weaned and on dry food (mix). That time is no earlier than 10 weeks and better at 12 weeks with two shots.
how much does he weigh?
lets hope for the best