Install nightly version copilot plugin - microsoft/copilot-intellij-feedback GitHub Wiki

Download a nightly plugin zip file from JetBrains Marketplace https://plugins.jetbrains.com/plugin/17718-github-copilot/versions/nightly
Follow JetBrains doc https://www.jetbrains.com/help/idea/managing-plugins.html#install_plugin_from_disk to install it.