.custom-switch .custom-control-label::before {
    width:50px !important; 
}

.custom-switch .custom-control-input:checked~.custom-control-label::after {
   background-color: #fff;
   transform: translateX(1.75rem)!important;
}

<header>
    <div class="container">
        <div class="row justify-content-center">
            <div class="col-md-5 d-flex ">
                <div  class="mx-auto">
                    <h3>> 1</h3>                
                    <h3>> 2</h3>
                    <h3>> 3</h3>
                    <h3>> 4</h3>                
                    <h3>> 5</h3>
                    <h3>> 6</h3>
                </div>
            </div>
        </div>
    </div> 
</header>