Severe diaper rash :(

Hey everyone, I’m a first time mom..21 years old with not a whole lot of experience taking care of babies (especially newborns). My baby developed a diaper rash and I didn’t notice until it was already pretty bad (the lighting in our house is pretty dim and it was in between her butt cheeks making it difficult to see. Do you have any suggestions in treating this at home ? Please help me , my daughter is in so much pain and it’s breaking my heart 😢, thank you in advance everyone!

EDIT// her rash is basically gone now ! Thank you everyone for your advice. In the end changing the diaper cream made a very big difference. Thank you !!