This study is for patients that have been diagnosed with platinum-resistant, high-grade serous epithelial ovarian, fallopian tube, or primary peritoneal cancer. The study is testing and investigational drug called INCB123667. "Investigational" means it has not been approved by the United States Food and Drug Administration (FDA). The primary purpose of this study is to evaluate the efficacy and safety of INCB123667 in terms of objective response rate (ORR) as assessed by an independent review committee (IRC). The drug is given to participants orally. Participants can expect to be on this study for approximately 24 months.