In https://www.suse.com/documentation/s...t_manconf.html,
the /etc/resolv.conf should not be edited by hand. Instead, it is generated by the netconfig script. To define static DNS configuration without using YaST, edit the appropriate variables manually in the /etc/sysconfig/network/config file.

So I edited like

systemctl restart wicked
cat /etc/resolv.conf

However I don't see the change in /etc/resolv.conf

Then I ran /sbin/netconfig update
And the output says : Attention: you have modified /etc/resolv/conf. Leaving it untouched. You can find my version in /etc/resolv.conf.netconfig (which contains the DNS server I added in /etc/sysconfig/network/config file).

I think I edited /etc/resolv.conf manually before the /etc/sysconfig/network/config test.

So at this point, if I would need to update DNS server info again, should I continue to edit /etc/resolv.conf manually or /etc/sysconfig/network/config?