Getting input from Gridview

In my database -

 

Header table :           Header_Id, Header_Name ,

Sub Header table :    Header_id, Sub_Header_Id, Sub_Header_Name,

Daily entry table:      Entry_id, Header_id, Sub_Header_Id, Entry_Date,  Amount

 

In Asp.net C# daily entry page:  User will select Date and Header from dropdownlist, I bind Gridview with respected sub header detail with amount(to get input from user) as template field column.

 

I want to save  this gridview data in Daily entry table, by click Save button from outside gridview.

 

I tried to save by using Viewstate and save all gridview record at once, but getting error.

 

Kindly suggest me to achieve this.