For home care you can use a warm/hot damp compress on the area to help it stay open and drain of infection. This will also stimulate blood circulation to help fight infection. You did trim the fur back away from the wound area to help keep bacteria out of the sore which is good! You can clean the sore out with Betadine iodine solution, chlorhexiderm solution, sterile saline, or 3% hydrogen peroxide. Then apply Neosporin or Triple Antibiotic ointment or cream to the wound or any scabbed over areas.
Keep the dog from licking the ointment off. It won't hurt the dog if it gets licked but it does better on the wound than on the tongue. A bit of peanut butter on the roof of the mouth can keep the tongue busy while ointment soaks in.I'd do this 2-4 times a day and if you see no improvement or the infection seems to spread see your vet for more care.
This might be a small puncture that got infected or a sebaceous gland that got clogged and then abscessed. Its better not to press on the lump as that can push infection into healthy tissue.
Hope this helps you!
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