Before proceeding, make sure you have the Theme and Required Plugins including the Elementor plugin installed.
Step 1: Login to your WordPress admin panel and navigate to Elementor → Settings
Step 2: Tick the other post you want to edit with Elementor in the Post Types section. If your theme has support for Header / Footer Builder make sure to check their corresponding post types.
Step 3: Update the other settings as you see fit and click Save Changes button.