Hi, im new to networking and mikrotik but trying to set up one more LAN in addition to two as described in schemes below

LAN1 utilizes RB750 as gateway to Internet, LAN2 uses other gateway and other Internet connection
Is it possible to set MT RB750 so LAN1 could use RB750 as a gateway and LAN3 could connect to Internet through the other gateway in LAN2?

I have already set up Wi-Fi bridge and tested it. We set up antennas in field and now im trying to connect to one RB/SXT through winbox from LAN1/3 but winbox does not detect RB/SXT’s MAC address
Yes it should be possible reference the articles on dual wan.
An easy fix could be just editing the DHCP Server info for LAN 3 and give it the other gateway.
Probably i dont know how to set up routes or firewall. i can ping the antennas from RB750 but can not ping them from a host in LAN3. i ve got an AS route 0.0.0.0/0 > Interface1 (WAN) in “routes” window. Should i create a new rule for LAN3? will the existing rule for 0.0.0.0/0 override new rule?
Thanks for any help
Okay for LAN 3 you need to mark those packets
IP/ FIREWALL / MANGLE
prerouting source address X.X.X.X/X (corresponds to the LAN 3 IP range) Action mark routing “Any Name”
Now you add your route
IP / Routes
dst 0.0.0.0/0 Gateway “The IP for second gateway” Routing mark “The name of the mark in the mangle rule”