In HandiTax, the Date of Birth (DOB) is entered in the Clients Details window. You cannot amend or adjust from within the Front Cover schedule of the Individual tax return:
Locate your client, then double-click to open the Clients Detail window
In the Client Details window, locate the Date of Birth field.
When you click into this field, enter the date manually or press F2 for the date picker option
Click Save then Close.