How to add host to dns server?

Question

Domain Name System

I have a router with openwrt firmware. There is an address like 1c.domain.com:3389 which refers to the same router, and then the router redirects the request to one of the machines on the network using PortForwarding. When the connection is made from the outside - everything works fine. When they connect to this address from the internal network, then the router naturally does not expect port forwarding on the internal interface and the connection does not occur.
The task is to make sure that the connection to the given address takes place both outside and inside the network. There is an idea to add an entry to the DNS server router so that 1c.domain.com refers to a machine inside the network, but I don’t know how to do this, please tell me.
If there is a more logical way to solve my problem, I'd love to hear it.
Thanks