This is a benign error. The error is only showing that the table cannot be deleted (dropped) because it's not present or has already been deleted.
To confirm that the nhConvertDb -finalize command completed fine, check the log file /opt/ehealth61/log/convert_finalize_<date.time>.log
and look for the completion message "DbTasksApp Completed".
You could also run the command:
echo "select state from nh_convert_state;" - sqlplus $NH_USER/$NH_USER
If this returns 0 then all is set correctly and the message can be safely ignored.
Wed 08:48:53 - nhConvertDb: drop table nh_unicode_convert
Wed 08:48:53 - *
Wed 08:48:53 - ERROR at line 1:
Wed 08:48:53 - ORA-00942: table or view does not exist