My baby had red patches around the chin too, mummy 😊 For us, it was mostly from drool and constant wiping.
What helped was applying a gentle moisturiser or barrier cream and keeping the area as dry as possible. Personally, I use Mama's Choice Baby Face Cream (not sponsored, I bought it myself 😆). It's quite affordable and helped reduce the redness quite effectively for my baby. ❤️
If it starts spreading or doesn't improve, I'd get it checked by your baby's doctor.