My Dog is have some reddish mark since last 2 days, this was not there earlier, thried finding if she got any heart but couldn’t find anything. What could it be.

Hi Raghavendra. It looks like a wound (blood stains are visible). Clip the hair around the lesion, clean it with betadine solution and apply betadine ointment for 7 days. But I would recommend you to see a vet for the proper diagnosis.