Demat accounts are very similar to your bank accounts.
When you opened ICICI demat, they would have sent you a book called DIS (delivery instruction slips). This is very similar to you cheque book for ICICI demat.
On this DIS slip from ICICI, mention the stocks and quantity you want to transfer. Similar to how you mention the amount on a cheque leaf.
Also on the DIS slip, you will need to mention where the stocks are being transferred to.
For this, you will need to mention details from the client master that you would have received when opening an account
- DP Name (In this case Zerodha Securities Pvt Ltd (not just Zerodha))
- DP ID ( For Zerodha securities pvt ltd, it is 12081600)
- Client ID ( this is your unique 8 digit number, your client ID will be mentioned on client master).
After filling all these details, submit the DIS slip to ICICI. They should ideally transfer all shares to the new demat within 24 hours.