define an HTTPS port under Administration -> My webMethods Settings -> Cluster Settings and modify the frontend url of MWS to point to https://hostname:https-port.
You will require a certificate which is placed under MWS/server/default/configuration/security.
The certificate should be packaged as PKCS12 (.p12) file and the trusted certificate chain should be packaged as a JKS file.
There is a demo certificate in the mentioned location as a reference.
Change the names of the certificate files in MWS/server/default/bin/server.properties.sh and profiles/MWS_default/configuration/custom_wrapper.conf .
See MWS Administration Guide for Details.