I have completed my graduation in Computer Science & Engineering. Now I want to change my discipline to History of Music. Is it possible? If so how? Please Help.

It seems highly unlikely you will be able to do this as the fields are so different - you would need to speak to your university and discuss your options

Some music courses are more humanities based than reliant on having any particular musical training so yes, it may be possible to get onto a music masters course without having done undergraduate study in it. It will be a particular type of music course that you'd be best to look at but still.