If you are not familiar with the oc command, refer to OpenShift - Getting Started with the oc command.
A node contains one or more pods, and each pod contains one or more containers.
The oc describe pod/pod_name command can be used to view a pods configuration.
oc describe pod/pod001
Something like this should be returned, in the JSON format by default. Notice in this example the JAVA_OPTS contains -Xmx512m and -Xms256m, meaning that the pods has 512 MB of memory allocated for the heap and 256 MB of memory allocated for metaspace.
Environment: JAVA_OPTS: -Xmx512m -Xms256m
The oc edit command can be used to edit the pods configuration.
oc edit pod/pod001
Let's say you update the pod to have 128 MB of memory allocated for metaspace.
JAVA_OPTS: -Xmx512m -Xms128m
After this change has been made, you will want to restart the pod (scale down, then up) for this change to take effect.