If you have performed all the installation steps and you still do not see the, you may probably need to "Clear Cache".
Standard cache clear: 'Einstellungen' > 'Caches / Performance' > 'Shop Cache leeren'.'
Still not seeing the Doofinder Layer?
Cache clear and compile themes: 'Einstellungen' > 'Caches / Performance' > 'Caches / Performance' > click the 'Cache' tab > Select all option from the screenshot > 'Leeren'.