Login to WordPress admin then go to Divi > theme options > custom css.
 
.page-id-1518 header#main-header {
display: none;
}

.page-id-1518 #page-container {
padding-top: 0px !important;
margin-top: -1px !important;
}


If you are unsure of the post ID then you can check this video on how to find it