роутер TPLink
192.168.1.50 -> 192.168.1.x/24
v
192.168.1.75
роутер Mikrotik
192.168.0.1 -> 192.168.0.x/24

/ip firewall mangle
add action=mark-routing chain=prerouting new-routing-mark=pptp_rm
    passthrough=no src-address=192.168.0.2-192.168.0.254
/ip firewall nat
add action=masquerade chain=srcnat dst-address=192.168.1.0/24 out-interface=
    bridge1WAN
add action=masquerade chain=srcnat out-interface=pptp-out1