Fail to route to gateway in different subnet

I’m totally new to Mikrotik and RouterOS and I seem to fail at accomplishing the following (see attached graph). I have the following setup:

  • Location A:
  • Subnet 1:
  • Network: 192.168.1.0/24
    • Gateway: 192.168.1.1
    • Subnet 2:
  • Network: 192.168.2.0/24
    • Gateway: 192.168.2.1
  • Location B:
  • Subnet 3:
  • Network: 192.168.3.0/24
    • Gateway: 192.168.3.1

At each location I have an additional MikroTik Router:

  • Location A:
  • MK 1:
  • Address: 192.168.1.254/24
    • Address: 192.168.2.254/24
    • Static Route: 188.144.0.0/12 → 192.168.2.1
  • Location B:
  • MK 3:
  • Address: 192.168.3.254/24

I need to accomplish that traffic of clients in subnet 1 & 2 to 188.144.0.0/12 is routed through gateway 192.168.2.1. I can only add static routes to gateway 1 & 3 (gateway 2 is totally off limits to me and cannot be altered in any way). Gateway 1 & 3 are very basic ones, I can only add static routes.

I tried:

  • Setting up an EoIP-Tunnel between MK 1 & MK 3 and adding a gateway route on MK 3 (188.144.0.0/12 → eoip-tunnel)
  • Setting up an IP-Tunnel between MK 1 & MK 3 and adding a gateway route on MK 3 (188.144.0.0/12 → ip-tunnel)
  • Configuring BGP on MK 1 (Networks 192.168.1.0 & 192.168.2.0, Peer 192.168.3.254) & MK 3 (Networks 192.168.3.0, Peer 192.168.1.254)

While clients in subnet 1 obviously work fine, I cannot get clients in subnet 3 working. The route always ends at MK 3. What would be the best approach to solve this, Tunnel, BGP, … ? Help needed and very, very much appreciated.
RoutingGraph_v1.png