Once all four digits are displayed on the screen, press and (or press the "OK" or "SCAN" button, depending on the model) for 2–3 seconds.
Several free or low-cost tools are available to calculate Incode from Outcodes
How to Program Ford Key Without Working Key - Auto Locksmith Boca
or those using specific outcode patterns (starting with 0040 or 0044). User Warnings and Best Practices Incode to Outcode for Ford/GM - Download