I would start with the Introduction, Intermediate, and Advanced fetal Monitoring courses offered by AWHONN before tackling the EFM certification from NCC. I’m currently studying for the exam myself and hear it’s pretty difficult even with L&D experience. The AWHONN courses will give you basic and foundational knowledge of fetal monitoring.
As far a studying for the exam, I’m using Mosby’s pocket guide to fetal Monitoring. Also they have practice questions on the NCC website and you can pay for practice exams on https://www.ccprwebsite.org/cp_product.cfm?i=200