The host DNS from /etc/resolv.conf is automatically set as a forwarder for the Samba DC as well. Reference
Generally, you can override smb.conf settings by editing include.conf from the config persistent Podman volume. For example, you can edit it with vim:
runagent -m samba0 # replace with your Samba MODULE_ID
podman unshare vim $(podman volume inspect config --format={{.Mountpoint}})/include.conf
However, the DNS forwarder is set as a command-line argument, making it more complex to override.
Why do you want to change the default behavior? It’s important to understand and evaluate your use case.