GitHub will show your new app's settings page. Note the App ID.
On the same page, generate and download a Private Key (.pem file).
Click Install App in the sidebar, install it on the organization or account you want Reili to investigate, and note the Installation ID from the URL (/installations/ID).
Set the environment variables:
GITHUB_APP_ID, GITHUB_APP_PRIVATE_KEY, GITHUB_APP_INSTALLATION_ID