Q: How can I use the "apple menu " if the keyboard and mouse aren't communicating with the computer?

The Bluetooth symbol on my iMac is flashing with a battery symbol.  I have replaced the batteries in my wireless keyboard and wireless trackpad (in the correct orientation) but none of these devices are communicating with the iMac --no response and the peripherals just keep flashing.  Instructions say to pair the devices by "clicking on the apple symbol".   How can I click anything if the trackpad and keyboard aren't in communication with the computer?