Navigate to the plugin configuration page, click the "Add New Provider" button (located either in the middle or top-right corner), select Discord as the application, and copy the callback URL from the plugin and keep it handy, as you'll need it to configure Discord as the OAuth provider.
After clicking on the New Application button it will show you the popup for providing a name to the application. Click on the Create button after providing the application name.
Navigate to the General Information section. Copy Client ID & Client Secret.
Navigate to the OAuth2 section & Add Redirect button for adding the callback URL from the plugin. Once done click on the Save Changes button.