Hi Amit,
LDAP authentication is part of MongoDB Enterprise edition which is a commercially supported product. If your organisation/company already has a commercial subscription I would suggest to open a case in the Commercial Support Portal. They would be able to provide you with the support required to set up with Cloud Manager.
Alternatively if you are evaluating MongoDB Enterprise and interested, send me a private message with your contact details and I can request a MongoDB Account Executive to contact you.
Regards,
Wan.