how i can to get chance dcs operator of boiler ?

FIRST YOU HAVE TO WORK IN BOILER FIELD AND KNOW THE ENTIRE PROCESSS AFTER GAINING THE FIELD EXPERIENCE .YOU HAVE TO KNOW THE INTERLOCKS AND LOGICS OF THE BOILER.YOU HAVE TO KNOW STARTING OPERATION PROCEDURE OF BOILER AND SHUTDOWN OPERATION AND COLD STATUP AND HOT STARTUP ,BLACKOUT OPERAATIONOF BOILER.

by studying and work in the field of the boiler

There are various courses for boiler operater, certified ppl only can.
Control from DCS, is advisable for ppl with sufficient training and expertise.