ask 50 people how to feed dogs you will get 50 answers

if this didn't start all of a sudden which could mean an actual illness or impaction or something then try feeding the dog give it about 10 minutes to eat then take away the food and offer it again about 12 hours later.....eventually they will eat.
I feed my dogs once a day because my first dog had food allergies and issues with not eating she actually ate more food and kept weight better going to this method and it was pretty common for her to go a couple days without eating.....for what its worth she ate only dog food I was in my dogs do not get people food phase of life and she lived 16 years ( a breed that 10-12 is common) total vet bills might have been 500 over her lifetime
go to a pet shop and see if they have samples of different feeds and try them out you can look into home made meals for dogs and raw feeding as well I have done all of them over the years....good luck