My mouse and keyboard are not working

The following will require any USB keyboard and mouse. If you don’t have them, borrow or buy them, they are inexpensive!

1. Connect the USB keyboard and mouse to the computer.
2. Open System Preferences – Bluetooth
3. Un-pair the wireless keyboard and mouse.
4. Turn off Bluetooth
5. Restart the computer in Safe Mode per the directions in How to use safe mode on your Mac - Apple Support
6. Restart the computer normally.
7. Open System Preferences – Bluetooth
8. Turn on Bluetooth
9. Re-Pair the wireless keyboard and mouse.
10. Unplug the USB keyboard and mouse and begin testing the wireless devices again.

Also, PLEASE read and follow the steps in Writing an effective Apple Support Commun… - Apple Community, your question has ZERO useful information for us. iMacs have been in production for 20+ years in hundreds of configurations and we have no idea what you own, the version of Mac OS, the keyboard and mouse you have etc...