Stuck with NAT problem

Hello friends (sorry for bad English).

I have dst-natted server in main office: xx1.xx1.xx1.233:80 >>> xx2.xx2.xx2.143:80
xx1.xx1.xx1.233:80 - Internal server’s IP.
xx2.xx2.xx2.143:80 - External server’s IP.
DNS records points on external IP only.

We have another (branch) office connected to main with SSTP tunnel.
All internal networks routed and see each other (just as local net).
My problem is: i need to connect to server by DNS name but to server’s INTERNAL IP.
branch office ip xx3.xx3.xx3.26

My topology:

[BRANCH] >>> [Main Office] >>> [Server]

I was trying to get things done wit hairpin NAT but no luck.
Can you give me advice to which way to look?

check this topic

https://forum.mikrotik.com/viewtopic.php?t=179343

HAIRPIN NAT INTRO

Unable to access your server via the DOMAIN name from the LAN???
Easily solved but every person will have to decide what is the optimal way to configure their device(s) for hairpin NAT (sometimes called Loopback).