Seems, you want to filter data of one DataTable into another (or even the same) DataTable.
If you would like to load filtered data into the same DataTable:
DT=DT.AsEnumerable()
.Where(x=>x.Field<string>("ImportTargetEntity")==Textboxvalue)
.CopyToDataTable();
DataGridView1.DataSource = DT;
If you would like to load data into another datatable:
DataTable AnotherDT = DT.Clone();
AnotherDT = DT.AsEnumerable()
.Where(x=>x.Field<string>("ImportTargetEntity")==Textboxvalue)
.CopyToDataTable();
DataGridView2.DataSource = AnotherDT;