To retrieve stock data, I always used:

Contract contract = new Contract(); //contract instance
contract.Symbol = "LRCX”; //ticker here
contract.SecType = "STK"; //contract type stock

That will point to the LRCX stock. However, IBKR manages the stock data using its unique contract IDs and it assigned a new contract ID to LRCX after its stock split on Oct 3 2024. So that contract instance will only point to LRCX after Oct 3 2024 and shows no such contract exists prior to the date. The current LRCX Conid is 732440574, but pre-split Conid is unknown.

When I pull up the chart on IBKR, it shows LRCX split-adjusted stock data for many years and clearly shows the split date, so its chart function is aware of the corporate actions and contract id changes, and retrieves data using both pre-split and post-split IDs.

To do that myself, I need the pre-action ID which I don't know. How can I pull up stock data before the split?