Edit the file /etc/systemimager/rsyncd.conf and put something like this into it:
#hosts allow = 127.0.0.0/24 MY_NET/NETMASK MY_CLIENT/32
hosts allow = 192.168.0.0/24 220.127.116.11/32
hosts deny = *
This will allow access from the subnet 192.168.0.0 and from the single machine 18.104.22.168; all other systems will be blocked.
Restart your SystemImager server afterwards: