Source: https://divisoup.com/move-divi-slide-menu-left/

Go to Divi > Theme Customiser > Header & Navigation > Header Format and select Slide-In from the drop down menu.

Desktop and mobile

    /*----------------------------------------------*/
    /*-----Slide-In Menu from Left by Divi Soup-----*/
    /*----------------------------------------------*/
    /*Move the hamburger menu to the left*/
    #et-top-navigation {
        float: left;
        padding-left: 0 !important;
    }
    /*Move the menu to the left when open*/
    .et_pb_slide_menu_active header#main-header,
    .et_pb_slide_menu_active #page-container {
        left: 320px !important;
    }
    .et_pb_slide_menu_active .et_slide_in_menu_container.et_pb_slide_menu_opened {
        right: auto !important;
        left: 0 !important;
    }
    /*Hide the screen overflow*/
    body.et_pb_slide_menu_active {
        overflow-x: hidden !important;
    }
    /*Move the logo to the right of the screen*/
    #logo {
        float: right;
    }
    /*Switch the slide-in animation from right to left*/
    .et_slide_in_menu_container {
        left: -320px;
        -webkit-transition: left 0.8s cubic-bezier(0.77, 0, 0.175, 1), margin-top 0.4s ease-in-out !important;
        -moz-transition: left 0.8s cubic-bezier(0.77, 0, 0.175, 1), margin-top 0.4s ease-in-out !important;
        transition: left 0.8s cubic-bezier(0.77, 0, 0.175, 1), margin-top 0.4s ease-in-out !important;
    }Code language: CSS (css)

Desktop only

/*Move the hamburger menu to the left*/
@media only screen and (min-width: 981px) {
#et-top-navigation {
    float: left;
    padding-left: 0 !important;
}
/*Move the menu to the left when open*/
.et_pb_slide_menu_active header#main-header,
.et_pb_slide_menu_active #page-container {
    left: 320px !important;
}
.et_pb_slide_menu_active .et_slide_in_menu_container.et_pb_slide_menu_opened {
    right: auto !important;
    left: 0 !important;
}
/*Hide the screen overflow*/
body.et_pb_slide_menu_active {
    overflow-x: hidden !important;
}
/*Move the logo to the right of the screen*/
#logo {
    float: right;
}
/*Switch the slide-in animation from right to left*/
.et_slide_in_menu_container {
    left: -320px;
    -webkit-transition: left 0.8s cubic-bezier(0.77, 0, 0.175, 1), margin-top 0.4s ease-in-out !important;
    -moz-transition: left 0.8s cubic-bezier(0.77, 0, 0.175, 1), margin-top 0.4s ease-in-out !important;
    transition: left 0.8s cubic-bezier(0.77, 0, 0.175, 1), margin-top 0.4s ease-in-out !important;
    }
}Code language: CSS (css)