One easy and common way to tell if a dog has a yeast infection is to watch for signs that your dog is constantly licking it's paws.
A dog that has a yeast infection will lick it's paws constantly.
Other signs that dog has a yeast infection are changes in color or texture of the fur and skin, odor, scratching and rubbing, head shaking and greasy or scaly skin.
When a dog has suddenly started to constantly lick his/her paws it's most commonly a sign of a yeast infection.
If the dog has just licked it's paws a few times then they are probably just cleaning their paws but when they constantly lick the paws it's not a good sign and when that happens your dog most likely does have a yeast infection.
A dog licking it's paws constantly can also be a sign of ear issues, stinky skin or weight issues and if it continues it would be a good idea to take the dog to the vet in case it has a yeast infection or other health issues.
If your dog does have a yest infection you can add a spoonful of coconut oil to your dogs food which can help kill the bacteria that causes the yeast infection in the dog.