Hi @diya_roy
To be best prepared for the exam review the exam study guide for the exam objectives, review more for areas that you are less experienced with.
Complete the learning path at MongoDB University, this gives the additional benfit of a discount for the exam.
Finally trying the practice questions gives an idea of what type of questions to expect.
refs:
https://learn.mongodb.com/learning-paths/mongodb-database-admin-self-managed-path
https://learn.mongodb.com/learn/course/mongodb-associate-dba-exam-study-guide/main/mongodb-associate-dba-exam-study-guide
https://learn.mongodb.com/learn/course/associate-database-administrator-practice-questions