All the front end layouts are done with Elementor. So you have to familiar with it.
If you’re new to Elementor. This page may be helpful for you
To edit a popup, go to “Templates (below Elementor) –> Popups”
Click on “Edit with Elementor”
To edit a popup, go to “Templates (below Elementor) –> Theme Builder”
Click on “Header” or “Footer” tab and proceed with the editing.