I have faced the same problem long ago. Below is the approach I have used best to my knowledge
First you need to recreate your dynamic control on PostBack as they no longer exist.
Then to get value submitted by user you need to use following syntax
Dim name As TextBox = DirectCast(tblMain.Rows(rowNumber).Cells(0).FindControl("txtName" & rowNumber.ToString()), TextBox)
name.Text = Request(name.UniqueID)
Hope this help and also let me know if you need some clarification