There are two ways to approach this problem.
You can change the port where GeoEvent Processor is listening for https traffic from 6143 to another port. To do this, find the file called "org.ops4j.pax.web.cfg". It is most likely in this path: "c:\Program Files\ArcGIS\Server\GeoEventProcessor\etc". Open this file in a text editor and around line 4 you should see where the secure port is being set to 6143. Change this to a different value (the default https port is 443), save the file, and restart your GeoEvent Processor in the Windows Services Control Panel. This will also affect the port you use to access the Manager.
The second option is to use a reverse proxy. The Web Adapter is designed for use with ArcGIS Server services (like Map Services or Feature Services), and has not been tested with the GeoEvent Processor's REST endpoint. You might have to use a different reverse proxy if this is the approach you need to follow.
