You most likely have the Apple 5.25 Drive Controller card in your IIe if you haven’t gone out of your way to get anything special to put in it since most all 8-bit Apple II software was released on 5.25 for the most part.
You’ll want to get a compatible controller for your 3.5 drive and put it in slot five:
From A2Wiki:
You need to have one of the following controller cards to use with your 3.5 drive:
Apple II UniDisk 3.5 controller, otherwise known as the Liron Card
Apple II 3.5 Disk controller, otherwise known as the SuperDrive Card. (as a bonus this card will work with HD floppy drives)
UDC / Universal Disk Controller (which will work with both 5.25 and 3.5 drives, DO NOT use this card with a ‘UniDisk’ 3.5” on this card, you’ll fry the card, just make sure your drive does not say “unidisk” on the underside)
Apple II Universal Controller
These cards can be difficult to find and costly. Personally, I’d get some Apple 5.25 drives and put that cash toward a CFFA3000 first as you can use it to load from disk images.
