Hello,
01. You can download the Slider Revolution in your account on our website here https://xtemos.com/my-account/
Install it via Dashboard -> Plugins -> Add new.
02. If you want to change the underline color of the menu items, you have to change the primary color of the site. Please go to Theme Settings -> Styles & Color -> Colors -> Change the primary color: https://ibb.co/Gfr3YddR
If you want to change only the underline color, then please use the below custom CSS code and paste it to Theme Settings -> Custom CSS -> Global CSS section:
.wd-nav[class*="wd-style-underline"] .nav-link-text:after {
background-color: red;
}
Best Regards