OWASP ZAP | ZAP Proxy | Cycubix Docs

You can change the ZAP port number by opening ZAP tools, going to options, and selecting local proxy. Learn how to change the default ZAP port with our quick ZAP guide

Change ZAP Port by opening ZAP, Tools–> Options –> local proxy. Change the default 8080 port to 8084 and you should be good to run both WebGoat (on 8080) and ZAP on 8090.