I can’t select the menu in my header on GTranslate (BizBoos Pro)

Hi, I'm trying to setup a multilingual website and I'm using GTranslate. Within the plugin you can select in which menu you want the button to appear (the flag you use to switch language),  but when I try to select one there are no menus available to pick. I'm not very familiar with FSE so am I missing something? The header is the default from the theme BizBoost Pro. Thanks!