Install the rsyslog-gnutls packge. In Ubuntu/Debian:
apt install rsyslog-gnutls

Add the following lines in the rsyslog file. In Ubuntu/Debian: /etc/rsyslog.d/50-default.conf or /etc/rsyslog.conf
$DefaultNetStreamDriverCAFile /root/certs/chain_bundle.crt
$DefaultNetStreamDriver gtls
$ActionSendStreamDriverMode 1 # run driver in TLS-only mode
$ActionSendStreamDriverAuthMode anon
*.* @@sgbox192.sgbox.it:6514

Restart the rsyslog service:
service rsyslog restart