It is common to manage WebLogic servers using a Node Manager. For more information about node managers see https://docs.oracle.com/middleware/12213/wls/NODEM/overview.htm#NODEM112

The easiest way to configure the JVM arguments is to add them from the example (mentioned in the controller installation guide) via the WebLogic console:

1. Login to the WebLogic admin console
2. On the left navigation click Environment->Servers
3. Click on the relevant server
4. Click on the Server Start table and fill in the Arguments field with the relevant JVM settings
5. Save and Restart the server