To change the argument separator in Excel from semicolon to comma:

1. Click on the Windows Start button and type "Control Panel" in the search bar. Click on the Control Panel app to open it.
2. In the Control Panel, click on "Clock and Region" or "Region and Language", depending on your version of Windows.
3. Click on "Change date, time, or number formats".
4. In the "Formats" tab, click on the "Additional settings" button.
5. In the "Customize Format" window, look for the "List separator" field.
6. Change the semicolon to a comma.
7. Click "OK" on all windows to save your changes.

Once you've made this change, Excel will use commas as the default argument separator in all functions. So, your example formula =IF(A10;B1;C1) will now be =IF(A10,B1,C1).