How to give JVM options for docker image - docker.elastic.co/elasticsearch/elasticsearch-oss:6.6.1

I am using the above mentioned docker image for building my elastic search cluster. After cluster build is finished, when I checked the Java process in the pod, it was taking default 1g as xms and xmx, I added in the elasticsearch.yaml config the JVM options as

ES_JAVA_OPTS: -Xms3000m -Xmx3000m

But, in this I am getting, no such config exists exception. What is the correct way to give the Java options in this image and where can I found the image specific documentations for elastic search?

In the java process, i can see

-Des.cgroups.hierarchy.override=/ -Xms3000m -Xmx3000m, this is coming. Is this overriding the heap size correctly?