configure router down dvb and up fiberoptic

hello
anyone have example or experience to setup router with condition, down from dvb (ISP A) and up with fiberoptic (ISP B) and i have block ip 203.x.x.x/21 from APNIC, i am confuse my IP from APNIC should advertise to ISP A and ISP B??? how to configure router in mikrotik??
i am use mikrotik 2.9.2

Thank you very much for the suggestion

DVB internal (PCI) or External?

hi, thanks for the reply
i am use dvb pci…
i am confuse on the routing…i get ip and gateway from ISP A ip:203.x.x.2 and gateway 204.x.x.1 and from ISP B i get ip:202.x.x.2 and gateway 202.x.x.1
ip and gateway ISP A i put on ether 1
ip and gateway ISP B i put on ether 2
on ether 3 i fill my ip from APNIC exp: 203.x.x.1 netmask 255.255.255.0

i m confuse because i got 2 gateway and ip from APNIC must advertise to ISP A and ISP B ???
could you give me an example ??? or a tutorial so i can learn that

thank you very much