My 50 day old rottweiler puppy don't like dog food ,
And became so week, how can I make him eat the dog food...

What does he like to eat? He's just a baby. Is he still nursing and with his mother?

He is probably about 7 or 8 weeks old, so weaned, and able to eat a good grade puppy chow for good nutrition and bone development. If he hasn't been away from the mother for long, then he may have to adjust to a puppy diet. Soften the dog food with some warm water and mix well.

Have you had him to the vet yet to be checked over and receive a schedule for his vaccinations?

No dog will starve himself/herself to the weakness stage.

She needs to be seen by a Vet.

A little background information would be helpful...

Has the puppy ever eaten dry food? Meaning has he suddenly stopped eating or has never eaten dry food?

How long have you had the puppy for? What did the breeder feed the puppy?

I personally would try soaking the dry food in warm water. Half a cup of water to 1 cup of dry food and leave soaking for half an hour.

If the puppy eats that then gradually decrease the amount of water you add so the food gradually becomes harder and the puppy gets used to eating hard food.