How to use a join in an insert statement and sql server

So I have two tables, landlords and property.

I am trying to insert data into my property table which works fine however I have to type the landlord id of whoever is logged in at that time in order for it to work. I was wondering is there a way to use an inner join with an insert statement.

I have previously done this using a select statement like so:

SqlConnection con = new SqlConnection();

con.ConnectionString = ConfigurationManager.ConnectionStrings["rent-dbConnectionString1"].ToString();

con.Open();

SqlCommand comm = new SqlCommand();

comm.CommandText = "select p.Property_Id, p.Property_Address, p.Property_Num_Of_Tenants, p.Property_Vacant from Properties p inner join Landlords l On p.Landlord_Id = l.Landlord_Id where l.Landlord_Id = p.Landlord_Id and l.Landlord_Email = '" + checkEmail + "'";

comm.Connection = con;

SqlDataReader rd = comm.ExecuteReader();

However, I am unsure how to use it for an insert statement as it is different than a select. This is my insert code at the moment:

string cs = System.Configuration.ConfigurationManager.ConnectionStrings["rent-dbConnectionString1"].ConnectionString;

SqlConnection con = new SqlConnection(cs);

SqlCommand cmd = new SqlCommand("INSERT INTO Properties(Landlord_Id, Property_Address, Property_Num_Of_Tenants, Property_Vacant) values('" + this.txtLandlordId.Text + "','" + this.txtPropertyAddress.Text + "','" + this.txtNumOfTenants.Text + "','" + this.chkVacant.Checked + "')", con);

con.Open();

cmd.ExecuteNonQuery();

con.Close();