One option would be to download the FREE Study Guide for the Magento 2 Certified Professional Developer Exam. For those who just missed passing, reviewing the scoring report and then taking time to study up on those areas has led to passing on a retry in many cases.
If you would like additional guidance and assistance in preparing for the Professional Developer exam, you should enroll in the instructor-led Magento 2 Certified Developer Study Group. This group is led by a Magento U instructor and meets one time weekly for 1.5 hours for 10 weeks to discuss and review exam topics.
Additionally, you can register to access the training videos in the Free Video Library.