how to redirect a network route on a mikrotik router or bras

I am still a newbie in mikrotik hardware.I have a task to redirect traffic in our network to point to a different mail server .We have two networks that are linked together thro a tunnel;and two ways to the internet.we have a microtik bras and a router in each site;It is the microtik bras that is used to direct traffic to the required route,the objective is to configure the the bras as on the attached map to be able to divert the traffic as needed;From the map,on normal occasion each site has its own way to the internet,but now there is work to be carried on the webserver in yaounde site,so I want to configure the bras not to send the traffic of users to the yaounde webserver for authentication,but instead send all yde traffic to use the douala webserver for authentication?And vice versa as same work will b done in douala webserver.Please i wish to invite anyone who is inspired to help me with the configurations on the different bras.
Augmentation ressource prod web2.pdf (91.3 KB)