header dropdown not working on mobile device

Not sure what happened but if you view the site on a mobile device it works where the top navigation is at the top and are listed vertical. The problem is looking at the submenu when you hover over the parent category link. Is it suppose to auto dropdown or I briefly see an image that looks like maybe you click but it doesn’t appear. Guessing maybe you click on this to show the submenu?

Is there a tutorial that helps identify how we can change this? We would also like to change the submenu image to a circle with a down arrow. What is the image name to look for?

Thanks for any info you can provide.