To help boost your dogs immune system you can feed them some fruits such as apples, pears, bananas etc and give them some Vitamin C and Vitamin D Supplements as well as some probiotics.
If your dog is having digestive issues then you should give the dog some probiotics daily for life or at least for 6 months or so and then wait awhile and see if they still are having digestive issues.
You can give your dog some probiotics daily to help improve their health.
However you don't have to give the dog probiotics daily unless you want too and it's okay to skip a week or so and then give them probiotics after you skip a week or so.
A dog can be given probiotics daily if they need them.
However usually just giving the dog dog probiotics once or twice per week is good enough to keep them healthy unless the vet says they need probiotics daily.
You're not gonna harm the dog though if you do give them daily probiotics if you want too give it to them that often.
When you give the dog probiotics daily or once or twice per week it will help with things such as inflammatory bowel disease, food allergies etc.
When you first give your dog probiotics it's recommended to give it to them daily and then after a month you can start giving the probiotics to them once every other day.