How to set up a virtual server on asuswrt-merlin?

Question

network hardware

Good for all! )
Combined two locales 192.168.x.0 with VPN (ping, connecting)
In the first 192.168.88.249:32400 server (plex)
In the second client on TV, which is looking for a server on its network (192.168.5.0, where the router is asuswrt-merlin, RT -AC66U, Firmware:380.70)
There is a connection from the second telnet to the server.
How to set up a virtual server on the asuswrt-merlin router at 192.168.5.1:32400 that forwards all calls from 192.168.5.0 to 192.168.88.249:32400 ?
I tried to write in /jffs/scripts/nat-start:
1.
iptables --insert VSERVER --table nat --proto tcp --match tcp --destination 192.168.5.1 --dport 32400 --jump DNAT --to-destination 192.168.88.249
By "iptables -t nat -nL" I saw the rule, but telnet to 192.168.5.1: 32400 is not connected.
2.
iptables --insert PREROUTING --table nat --proto tcp --match tcp --destination 192.168.5.1 --dport 32400 --jump DNAT --to-destination 192.168.88.249
by "iptables -t nat -nL" did not see the rule, telnet does not connect ...
Therefore, 2 questions:
1. What should I do? (Who is to blame is understandable!)
2. Where to read? (Yandex gives little on the topic, it’s difficult with English (and Yand is not enough), I read it here - www.opennet.ru/docs/RUS/iptables , but merlin’s is wider, but I didn’t find details on his wiki ... ((
pc. via do not offer plex.tv - the first network behind the evil provider nat!