Save the old Kafka configuration and add symlink from /etc/kafka/conf:

mv /etc/kafka/conf /etc/kafka/conf.saved

ln -s /usr/hdp/current/kafka-broker/conf /etc/kafka/conf

ls -la /etc/kafka

total 4 
drwxr-xr-x 3 root root 4096 Jun 19 21:51 2.3.0.0-2323 
lrwxrwxrwx 1 root root   35 Jun 19 21:54 conf -> /usr/hdp/current/kafka-broker/conf 
drwxr-xr-x 2 root root 4096 Jun 14 00:11 conf.saved

From Ambari Web, browse to Services > Kafka.

From the Service Actions menu, select Start.

Copy the Kafka .properties files from the HDP 2.2 configuration directory into the HDP 2.3 configuration directory.

cp /etc/kafka/conf.saved/tools-log4j.properties /etc/kafka/conf/

cp /etc/kafka/conf.saved/test-log4j.properties /etc/kafka/conf

cp /etc/kafka/conf.saved/zookeeper.properties /etc/kafka/conf/

cp /etc/kafka/conf.saved/producer.properties /etc/kafka/conf/

cp /etc/kafka/conf.saved/consumer.properties /etc/kafka/conf/