Hello,
Do you want to change the header? Use Header builder https://www.youtube.com/playlist?list=PLMqMSqDgPNmDu3kYqh-SAsfUqutW3ohlG To change footer edit Static Blocks https://youtu.be/gY-x4m47Duo but instead of the WPBakery builder from the video use Elementor (Elementor > Settings > enable it for the Static Blocks).
Regards
