Well, you don't indicate whether or not your tables/schemas are the same, but on the premise that they ARE the same,
1) Add your datatables dt, dt1 to a dataset
2) Bind your gridview to one of the datatables
3) In the SQL command used to select data, join dt, dt1 on a key
If your tables/schemas are different, 'merge' the dataables DataTable.Merge Method (System.Data) | Microsoft Docs
] or you may wish to manually create a 3rd datatable and populate that using a SQL insert selecting and joining the data as required from the two 'base' datatables'