How to insert multiple rows into a sql server, keeping all these rows in the same id

Question

I am studying a program that lends equipment, in its proper functioning, when making a loan of material should be kept in the dbo.emprestimo all loan details (name, location, business, etc), then update dbo.equipamento to make that equipment "unavailable", and finally add all borrowed equipment in a third table dbo.item, where all borrowed equipment would be stored followed by the idEmprestimo for future consultation (similar to a supermarket purchase in which has the code of each purchase saved and within the code of the purchase has all products purchased).

The part about saving dbo.emprestimo and update the dbo.equipamento I am managing to do without problems, but the last part of saving the equipment in a third table dbo.item with the same loan id. I’m having a lot of trouble, I’ve been a few months idle and I’m a little rusty, I thought of something like:

code inside save loan button:

for (int i = 0; i < dataGridEmprestimo.Rows.Count; i++)
{
    SqlConnection con = new SqlConnection(@"Data Source=localhost\SQLEXPRESS;Initial Catalog=Ianes;Integrated Security=True");
con.Open();

    SqlCommand cmd = new SqlCommand(@"INSERT INTO item (idEquipamento,idEmprestimo) VALUES ('" + dataGridEmprestimo.Rows[i].Cells[0].Value + "','" + HERE + "')", con);
    SqlCommand cmds = new SqlCommand(@"UPDATE equipamento SET equipamento.status = 'Indisponível' WHERE equipamento.id = '" + dataGridEmprestimo.Rows[i].Cells[0].Value + "'", con);

    cmd.ExecuteNonQuery();
    cmds.ExecuteNonQuery();
    con.Close();
}
            

Where the value "HERE" should be the value of the loan id, I thought of something like:

SELECT max(id) emprestimo

But I’m not getting a good result, I hope you understand.