Greetings! If you could please post a link to your site, I can help you pinpoint what to change. But also, just to confirm…you want to reduce the space just above the menu only or the whole top header area?
I have to say thank you because you just found a mistake on my part. There should be a theme setting to adjust the menu container with a margin. If you contact me from my website, I will send you a fix for this.