Hi,
the margins for the slider can be set using CSS files.
For instance in /themes/yourtheme/assets/css/custom.css
@media (max-width:1200px){ #index .carousel .carousel-item img {width:125%;} #index #carousel h2{margin-left:-200px} }
However the best thing to do, IMHO, seems to edit the first slider image: crop it or add the exact margins you want, in order to obtain the same size as the other pictures.
(There are free and efficient tools that can do that, such as https://www.gimp.org/ )