Hello, I hope I can be of some help.
The types of skin lesions you are describing could have a number of causes, and the diagnosis and best possible treatment would be ideal, by visiting the vet. However, if the area is not bothering your dog right now, I think there are a few things you could try at home to see if it helps. If not, certainly you would need to see the vet.
Based on your description and the location of these sores, I would be most suspect of a surface bacterial infection on the skin, which we call "superficial pyoderma." Of course, I can't diagnose online but this is my best guess! This will cause round crusty scabby spots, especially in the groin and on the belly area, and often does not seem to bother the dog. However, it can be itchy sometimes. It is very common especially in the warm time of year, or if the dog has any underlying skin problems such as allergies. It is not contagious, but rather caused by an overgrowth of staph bacteria, which are normal on the skin.
In some dogs it seems to cycle and resolve on its own. However, if diagnosed at a vet's office it is usually treated by oral antibiotics. That would have to be by prescription, but what you can try at home would be an anti-bacterial, medicated dog shampoo, such as Pyoben. These shampoos tend to have benzoyl peroxide and help control bacteria. The vet would definitely have an anti-bacterial shampoo available which they should be able to sell you over-the-counter. You may be able to find an anti-bacterial shampoo at a pet supply type of store too, but I can't guarantee the quality. With these shampoos, typically the dog needs to be lathered up and then let the shampoo soak in for 10 minutes before rinsing. I have seen some dogs clear up with a shampoo alone. Depending on the number of sores, the areas can be treated with topical antibiotic ointments such as bacitracin or neosporin as well. That may be a lot of ointment if there are lots of sores!
Here is some information on pyoderma:
In the article you will see that there can be a number of underlying causes, such as parasites or allergies. If the sores get much worse, your dog starts to itch, or it is just not improving, obviously a visit to your vet is in order to get to the bottom of it and see if there may be something else going on.
I hope this helps! Thanks for your question! Best of luck to you and your dog :)