IPTABLES FORWARD Remote desktop connection via

I would like to forward internet requests for a terminal server running RDP (Port 3389) from the Public IP to the internal windows server
i used the rule
iptables -t nat -I PREROUTING -d 19x.xxx.xxx.xxx -m tcp -p tcp --dport 3389 -j DNAT --to 192.168.x.x:3386

I cannot remote desktop into the computer

Can anyone help?

thanks