The Bosch air handler has dip switches inside to change the fan speed. The unit I have is very similar to the Bosch. You can have a look at this manual to familiarize yourself https://resource.bakerdist.com/is/content/Watscocom/Gemaire/bosch_8-733-952-441_article_2674327384527413_en_ii.pdf

The issue I have with some installers if that they won’t spend the time to set up each system to each home. Most will just install and not set settings for comfort or efficiency.