Hello east_ikebukuro
Thank you so much for contacting us!
You can manage your megamenu static block by going to Dashboard > Appearance > Menu and click on 8Thme Category Options https://prnt.sc/10gcjs2 and select your static menu https://prnt.sc/10gcxbs .
We are also sharing Video Tutorial For header builder
https://www.youtube.com/watch?v=RbdKjQrFnO4&list=PLMqMSqDgPNmDu3kYqh-SAsfUqutW3ohlG
If this doesn’t work or you have more questions, just let me know, and I’ll be happy to help!
Robert Hall
Customer Support