This is fairly easy to do with an sql command and a delete statement.
Assuming your text file is inserted into a SQL database. You could do something like:
using (var sc = new SqlConnection(ConnectionString))
using (var cmd = sc.CreateCommand())
{
string value = "%^00000570642^%"
sc.Open();
cmd.CommandText = "DELETE FROM table WHERE textField like @value";
cmd.Parameters.AddWithValue("@value", value);
cmd.ExecuteNonQuery();
}
Is this what you were after?