I want to take my iMac in to recycle

You should be able to just take it in. https://www.apple.com/recycling/nationalservices/ I doubt you need an appointment, but you might want to call the store to ask if there might be a preferred time.

Hello, Auntterri.

No, you don't need an appointment to drop off your Mac for recycling.

But, before you do that, please have look at this link–

What to do before you recycle your Mac - Apple Support