This is a clinical study that has two parts. It is testing a potential new medicine called Sofetabart Mipitecan (LY4170156) for people with certain types of ovarian, peritoneal, and fallopian tube cancers. Part A looks at participants whose cancer no longer responds to platinum-based treatments (a type of chemotherapy). Part B looks at participants whose cancer still responds to platinum-based treatments. The researchers want to find out if Sofetabart Mipitecan works better than the usual treatments that doctors use now and to better understand how safe it is. Each participant's time in the study will depend on how they respond to the treatment.