You can actually return the phone within 15 days as long as its in resellable condition and you have all the stuff it came with. The rep can then reactivate your old phone.
If you can't return it then you can still go back to your old phone. Log into Self Serve, go to Mobile Phone Tab, and then select swap phone and follow the instructions.
If your old phone doesn't use a SIM card then keep in mind by next year the network it uses will be shut down so you're going to have to upgrade eventually.
What didn't you like about the iPhone? Touch screen? Size? Price? There's many Android options available you can look at. If touch screen was your issue, Koodo doesn't carry any keyboard phones anymore because the market/demand has dwindled for that. You're better off buying a compatible phone on eBay or Kijiji,etc.