The Exam page https://learn.mongodb.com/pages/mongodb-associate-developer-exam contains many links to resources to get ready for the exam.
First among these is the learning path, this alone is excellent training: https://learn.mongodb.com/learning-paths/mongodb-python-developer-path
The Study Guide: https://learn.mongodb.com/learn/course/mongodb-associate-developer-exam-study-guide/main/associate-dba-exam-study-guide
And Practice Exams: https://learn.mongodb.com/pages/mongodb-developer-practice-questions
With all of these you will be well prepared for the exam.