How to distribute LTE Internet in VPN on Mikrotik?

Question

Mikrotik

There is a Mi-router that receives and distributes the Internet from the provider and has a white external IP. Mikrotik (ether1) with an LTE modem is connected to it. On Mikrotik, a PPTP server has been raised that listens to ether1. The Mi router is configured to forward ports 1723 and 47 to Mikrotik. Mikrotik receives the address 192.168.1.250 on ether1 from the DHCP mi-router. The LTE modem has its own DHCP server and issues Mikrotik to the LTE interface with the address 192.168.3.100.
From a remote server I connect via PPTP to Mikrotik using the external IP address of the mi-router successfully, the connection is established, but the server does not receive Internet from the LTE modem. Question: how can I direct the Internet from the modem to the VPN connection?

UPD: added a diagram

Answer 1

Change the Mi-router to the second Mikrotik and configure the ports