Here's a post that might help - https://www.petbasics.com/dog-education/how-to-get-rid-of-fleas-on-dogs/
Bathe in original blue Dawn dish washing soap. A tip from a groomer over 25 yrs ago. Not one flea since!
Once you give them a flea bath, do another flea bath a week later. There are combs for dogs known as flea combs, but you need to get the fleas to die and check for any flee eggs
Give your dog a good flea bath then a flea spot that will kill all stages of fleas. Don't forget to treat your home too. We had good luck with this https://amzn.to/2N6lGM2