[Help] How to get internet access from another router

RouterOS Beginner Basics
1

Halo

I have 2 router (A and B) which router A connected to ISP (eth1) and the other ethernet, eth2, eth3, eth4, eth5 can access internet. Then router A (eth3 192.168.3.1) and router B (SFP1 10.16.11.1) connected by converter (optic to FO). I try to routing to have internet access on router B (eth2 10.16.2.1 and wlan1 10.16.12.1) but the route does not reachable

Thank you for solution

2

Then router A (eth3 192.168.3.1) and router B (SFP1 10.16.11.1) connected

Router B connected to Router A ? That link should be in one IP subnet, Probably 192.168.3.0/24.
Many IP subnets in this partly described setup. Using routing tables in Router A or extra NAT in Router B? For Router A - Router B networks. Where is NAT used?