The billboard effect is when a traveller discovers a property through a third-party booking channel, such as an online travel agency (OTA), metasearch site such as Tripadvisor, Trivago, Kayak etc. then looks to book directly with the property.
Utilize the benefit
Get more traffic to your website. The more traffic to your website will help increasing the rank on search engine. Make sure your website has mobile responsive design and protected by https/ssl security.
Inform your value better. Most of OTA and metasearch site provide basic information about your property, so use your website to tells your property's unique selling points such as location, near popular attractions, and any other reason why the traveller must choose your property over competitors.
Revenue maker. Integrated your website with a real-time booking engine, and offer better rate/value for direct booking, so the traveller prefer to book on your brand website and can book instantly.
If your property don't have a huge advertising budget or part of big chains hotel brand, you can utilize this effect to promote your hotel brand. Each OTA and metasearch site have their own strong market, so the more you have the stronger effect that you can get.