how to only route my vpn trafic to specific address not others

hi dear members

as i am new here i would like to ask some expert that how can i route my vpn traffic to my specific ip series and dont disturbed other ip series .
i am using pptp vpn server at my main site where i am also using other utilities like bridges, sip telephone on same network with different ip series i want that my mikrotik rb750 just connect to my local network with ip series 192.168.0.* and for bridges i use 172.172.0.0 series and for sip i use 192.168.3.0 series but when i plug rb 750 router board all my sip telephone and bridges gone down so plz help me out how can i route my traffic to only 192.168.0.0 and my others ips series and utility dont disturb
waiting some expert help