Kindly help with steps to configure S/MIME certificate
Have you had a look through this resource? https://help.anaplan.com/23410167-f022-41fb-9f77-93c66e8e409f-Administration:-Security---Certificate...
Alternatively @riyazpasha might be able to help. It is quite a fiddly process!
Please go through the below training for the conversion and procuring of the CA certificates.
Interactive CA Certificate Guide - Anaplan Community
Let me know if you need any help on the same.