It is better to push routes from openVPN server, you can see on this page http://forum.mikrotik.com/t/clients-in-mikrotik-cannot-access-debian-openvpn-server/64660/1 , then you needn’t manually add static routes to all ovpn clients … if isn’t for you then you can add routes for address as first one:
dst address - destination address, gateway - ovpn client interface “ovpn_out1” is for me, other options are default