iTunes Wi-Fi Sync with iMac

I have switched from a Macbook Pro to an iMac and I have iTunes on an iPhone 6 and an iPad. I have set up Wi-Fi Sync on the iMac (followed the instructions to attach to IPhone to the iMac, etc), but in the Systems/ General/iTunes Wi-FI Sync page on the iPhone there is a message that says "Sync will resume when "Bruce's Macbook Pro" is available.

I've erased all content on the Macbook and sold it through Apple. How do I switch to the iMac?