imac has disconnected from wireless keyboard and track pad, no way to click login icon

Follow the steps at > https://support.apple.com/en-us/HT204621

If that does not help? Dig out, borrow, buy a USB keyboard and mouse to continue on and reconnect your wireless devices. Also FWIW, most any inexpensive Generic or PC keyboard and mouse will work with a Mac.

If you have an Apple Magic Trackpad 2, and Magic Keyboard 2, you can simply connect them to your Mac with a Lightning cable, and they’ll operate via USB.