Diet for new shepherd owner

hello i am new to german shepherds and this is my first one. He is 8 months old and his name is Scout. i have had him for 4 months and when i first got him he was a full puppy. After a month or two i noticed he was not holding his weight. He started being crate train but then moved outside for a month due to issues at the home with remodeling. Now we are bringing him back in but he seems underfed according to his new trainer. The first trainer told me to feed him 1 1-2 to 2 cups of food 2 times a day. The new trainer said at 8 months that he should be at least 50-70 lbs and he is at about 38 and the vet said he has no health issues. I was given a diet and wanted to see if anyone else had this issue before.
His new diet is 4 cups of food to start and a cup of milk and for day one raw meat at both feedings. if he eats all of his food fill the bowl back without milk and let him continue until he is full. let him stay on his lease outside for about an hr and put him in his crate until dinner feeding. Repeat this for 2 weeks to see if he can put on weight.

Like i said i am new to shepherds so i was given misinformation and have a border-line healthy dog. Any help or advice given would be greatly appreciated.

Thanks