How to remove whitespace on mobile version, above video background, under header on home page... HELP ME PLS!!

#1. Try adding to Design > Custom CSS

@media screen and (max-width:767px) {
[data-section-id="62bc52cd38628f69914e5f38"] iframe {
    width: 100% !important;
    height: auto !important;
    left: 0 !important;
}
[data-section-id="62bc52cd38628f69914e5f38"] {
    min-height: unset !important;
    margin-top: -100px;
}
}

#2. Can you send all current code in Code Injection & Page Header?