This pup is really young, he still neds to be with the litter mates. This is the age that he needs to be weaned. It is easy to wean a litter than a single pup as survival of the fittest kicks in, this encourages thes pups to eat.
Is the pup able to lap milk, if so give milk for starters, he is stil too young.
Buy the way, puppies taken away so young usually have beghavior problems as the do not learn pack behavior.
The consistancy of the cerelac is very important. it should just there so that it does not stick in the pups mouth, usually the upper mouth where the pup is unable to retreive as he is still you.
Make it very watery to start with, when he can eat cerelac from the dish by himself, make the formula thicker then switch to commercial dog food for a few weeks then to the diet u plan to give him.