my track pad will not connect to iMac - without this ability how do I make a correction ? iMac is essentially unusable without mouse.

The iMac will need some user input device, whether you acquire a wired mouse (recommended), or resolve the pairing issue with your Trackpad. If it is the older replaceable battery Trackpad, then replace the batteries, or if newer rechargeable Trackpad, ensure it is fully charged. In either case, switch off the Trackpad, shutdown the iMac, switch on the Trackpad, and boot the Mac. Click once on the Trackpad when your Desktop appears and see if you get the notification that the device is connected.