Save the old Knox configuration and add symlink from /etc/knox/conf:

mv /etc/knox/conf /etc/knox/conf.saved

ln -s /usr/hdp/current/knox-server/conf /etc/knox/conf

ll /etc/knox

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/knox-server/conf
drwxr-xr-x 2 root root 4096 Jun 14 00:11 conf.saved

From Ambari Web, browse to Services > Knox.

From the Service Actions menu, select Start.

After Knox has started, select Run Service Check. Confirm the Check passes.