In that case, besides you need to be familiarized with docker setup (the above links refer to SOLR in Alfresco 5). You should customize your own docker-compose configuration in docker-compose.yml, for example using custom environment variables in solr6 image, forwarding to a different port, or mounting the corresponding configuration directories for SOLR locally such as solrcore.properties or shared.properties, it depends on what you want to config...
ng-office-ass_1 | Error: Could not find or load main class contentstore ng-office-ass_1 | Caused by: java.lang.ClassNotFoundException: contentstore
A also tried to add this property as a new "JAVA_OPTS" entry. I didn't get any error message, but after I checked solrcore. properties file in my ass container I can see that alfresco.cron property is the same.