If I understand you correctly, you want hosts on the internal network accessing your local server using the domain name?
As jggimi stated, a method of configuring this could be to have your DNS serve the internal address to clients on the Internet network.. however the following should be adequate to rewrite requests from your LAN to your external IP and replace them with the address of your internal service.
Code:
match in on $int_if inet proto tcp from $int_if:network to (egress:0) \
port https rdr-to $websrv