It appears to be "Ear Canker" which could one of several types of bacterial infections. Taking the hen to a vet would be best to determine what bacteria and antibiotic treatment would be best to clear it up. Here's a link:
https://www.chickenwhisperermagazine.com/health-and-wellness/ear-canker
https://www.chickenwhisperermagazine.com/health-and-wellness/ear-canker
