The shares have to be dematerialized first in the respective share certificate holder’s Demat account.
If it is a joint share certificate, then a joint Demat account has to be opened and the physical certificates have to be dematerialized here.
Once the shares are available in the Demat form in their respective accounts, a DIS(Delivery Instruction Slip) of the concerned broker has to be filled with the share details meant for transfer.
You have to provide the Demat details(DP ID and DP Account Number) of your target Demat account to that concerned broker processing the DIS slip and the shares will then be transferred to your account.
This is Zerodha’s Dematerializion Request Form.
And this is how you typically fill a DIS slip.