* LEGO Harry Potter: Years 1-4 (2010): Trailers can be found on YouTube by searching "LEGO Harry Potter Years 1-4 trailer."
* LEGO Harry Potter: Years 5-7 (2011): Trailers can be found on YouTube by searching "LEGO Harry Potter Years 5-7 trailer."
* LEGO Harry Potter: Collection (2016): This is a remastered collection of both the Years 1-4 and Years 5-7 games. Trailers can be found on YouTube by searching "LEGO Harry Potter Collection trailer."
To find a specific trailer for the game you're interested in, you can use the search terms above and refine your search by adding keywords like "official trailer," "gameplay trailer," or "launch trailer."
If you're looking for a trailer for a specific movie adaptation, it's unlikely to exist as there haven't been any LEGO Harry Potter films produced.