Refer to this Knowledgebase article for configuring kubelet logging verbosity.
In this example, I have followed the article to create MachineConfigs to apply the logging level to /etc/kubernetes/kubelet-env which will persist across reboots.
Then, I applied the MachineConfigs to the cluster with:
oc apply -f 02-kubelet-env-config-master.yaml
oc apply -f 02-kubelet-env-config-worker.yaml
oc apply -f 02-kubelet-env-config-infra.yaml # for clusters with infra tier