Hi Chris,
ok, so looking at it you need to set your logo in the Customiser > Layout > Primary Navigation (and remove the Site Identity one) and set this to sticky and static. Whilst there you can align the navigation center. Thats 90% of it.
The fixed call button, can be added as a menu item. Follow this article to assign the item a class:
https://docs.generatepress.com/article/using-the-wordpress-menu-builder/#custom-classes
then you can target that selector and style it with CSS. To begin with making it float right would be:
.your-custom-class {
float: right !Important;
}