There is really no direct support for MongoDB in WebSphere. The application will be handling the driver directly and with that there is really no direct configuration set up needed from WebSphere side. MongoDB cannot be used in WebSphere Application Server as a JDBC Provider and data source as other full databases like DB2 and Oracle can.
Instead, MongoDB must be accessed through MongoDB APIs and configured per this document:
https://www.ibm.com/docs/en/was-nd/8.5.5?topic=ddaa-porting-liberty-application-that-uses-mongodb-full-profile
#Support#SupportMigration#WebSphereApplicationServer(WAS)