Implement QoS for 3CX VoIP on Debian Linux

[Phm]

This link https://www.3cx.com/blog/voip-howto/qos-linux/ details how to impement permantly QoS on Debian Linux 3CX V18. Alas, V18 has changed the location of the files and I confess I'm quite lost.

I was able to issue the commands:

iptables -t mangle -A OUTPUT -p udp -j DSCP --set-dscp 56
iptables -t mangle -A OUTPUT -p tcp -j DSCP --set-dscp 56

Now the problem is to make this change permanent and I've read that V18 stores these settings in nftables. I'm stuck at this point. I'm kindly asking to the Linux gurus if they can just type this command so I can make the settings permanent.

Thank you in advance.