Whenever you wanted to transfer your shares from DP to another, the delivery instruction slip (DIS) book is mandatory
suppose if you have an demat account with “X” broker those shares you willing to transfer to “Z” broker, you need to visit the X office with DIS book in that slip you have to fill the your shares details along with isin number & Z broker DP id also, it will take maximum 24 hours to transfer, for transferring of shares broker’s may charge for this