Configure the Minimalist application, which has a similar setup, and change the embedded code to point to this location instead of the web maps URL.
Steps:
1. Open the web map.
2. Click Share.
3. Click CREATE A WEB APP.
4. Search 'Minimalist', and create the Minimalist application.
5. Configure the Minimalist application with Home button.
6. Copy the application URL.
7. Navigate back to web map.
8. Click Share.
9. Click Embed in Website.
10. Check Home Button and copy and paste HTML.
11. Replace the web map URL with the application URL.