Consider The Causes
It's always important to first rule out any health concerns that may be attributing to your puppy or dog's lack or food motivation. Health issues like IBD (inflammatory bowel disease), pancreatitis, and even anxiety can contribute to your pups poor appetite. These issues can be ruled out at your veterinarians office. If you notice any physical signs of illness like vomiting, diarrhea, or lethargy, it's a good idea to contact your vet asap as these issues are not likely to be resolved on their own. Sometime it may be an allergy that's causing your dog to have adverse reactions and feelings towards food. In these cases, it may be as simple as switching food proteins to resolve the problem. For example, if your dog's eating chicken flavored food, switching to beef or lamb may be an easy quick fix for them.
If you've already tried switching different food proteins and are still having issues, then even if you're not seeing psychical symptoms, it's best practice to make a vet visit to rule out any potentially harmful illnesses. You vet may also prescribe a special diet that can help your fur baby to get back on track.
Are You Using Food in The Best Way?
The next major factor to consider is if you are using food in the best possible way. If for example, your puppy is allow to "free feed" meaning they have unlimited access to food at all times, then you can see how food but not have as great of a value. There's a simple solution to this as well, having set feeding times and limited portions of food at these times. This will make food hold more value for your dog.
You may also be using food in a way that's not valuable to your puppy, by choosing a food they don't like. Most dog's will not find kibble nearly as valuable as wet food, real meat, or even cheese. These foods are much higher in flavor and tend to be more popular around pickier dogs. They usually will gravitate toward foods or treats that are moist as well. Trying to use your puppy's kibble as treat rewards may be a convenient solution, but it may also be why your puppy is not eager to work hard for you. Try adding in some different flavors, textures, and foods that are more moist.
Think About Alternatives for Puppy Training Success!
It's important to keep in mind that there are alternatives to using food as a reward. During training it's usually easiest to use food as your reward, but this is not always an option so it's good to think abut alternatives that may work better for your pup. For example, praise is a huge reinforcer to most dogs. Don't underestimate the power of a "GOOD BOY!!." In addition, some dogs prefer play as their rewards. You can use games like tug or fetch as their reward for doing a behavior correctly. This is a common staple in dog training for service dogs, search and rescue dogs, and police dogs. Because you won't always have easy access to food rewards, it's good practice to use alternative forms of rewards.