Save the old Flume configuration and add symlink from /etc/flume/conf:

mv /etc/flume/conf /etc/flume/conf.saved

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

ls -la /etc/flume

drwxr-xr-x. 3 root root 4096 Jul 11 22:20 2.3.0.0-2551
lrwxrwxrwx. 1 root root 34 Jul 14 13:19 conf -> /usr/hdp/current/flume-server/conf
drwxr-xr-x. 2 root root 4096 Jul 11 20:46 conf.saved  

From Ambari Web, browse to Services > Flume.

From the Service Actions menu, select Start.

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