Add to the div element inside the li element the class "h-100":

<section id="l4l-pickup-how-it-works" class="px-3 py-4 p-lg-5">
    <div class="container mt-5">
        <div class="text-center mb-2">
            <h2 class="display-5">How It Works</h2>
        </div>
        <ul class="row list-unstyled g-3" style="min-height: 100px; padding-top: 2vmax; padding-bottom: 3vmax;">

            <li class="col-md-4 d-flex flex-column align-items-start p-3 mb-4">
                <div class="cmg-bg-primary rounded p-4 d-flex flex-column">
                    <div class="d-flex justify-content-center align-items-center border rounded-circle bg-light" style="width: 100px; height: 100px; font-size: 24px; font-weight: bold;">
                        1
                    </div>
                    <h5 class="mt-3">Tap the “Schedule Pick Up” button to get started!</h5>
                </div>
            </li>

            <li class="col-md-4 d-flex flex-column align-items-start p-3 mb-4">
                <div class="cmg-bg-primary rounded p-4 d-flex flex-column">
                    <div class="d-flex justify-content-center align-items-center border rounded-circle bg-light" style="width: 100px; height: 100px; font-size: 24px; font-weight: bold;">
                        2
                    </div>
                    <h5 class="mt-3">Our driver will send you a text when he is en route at the time you schedule</h5>
                </div>
            </li>

            <li class="col-md-4 d-flex flex-column align-items-start p-3 mb-4">
                <div class="cmg-bg-primary rounded p-4 d-flex flex-column">
                    <div class="d-flex justify-content-center align-items-center border rounded-circle bg-light" style="width: 100px; height: 100px; font-size: 24px; font-weight: bold;">
                        3
                    </div>
                    <h5 class="mt-3">Our attendants will weigh, prep, and process your items to your specifications</h5>
                </div>
            </li>

            <li class="col-md-4 d-flex flex-column align-items-start p-3 mb-4">
                <div class="cmg-bg-primary rounded p-4 d-flex flex-column">
                    <div class="d-flex justify-content-center align-items-center border rounded-circle bg-light" style="width: 100px; height: 100px; font-size: 24px; font-weight: bold;">
                        4
                    </div>
                    <h5 class="mt-3">Once cleaned, folded, and packaged, our driver will notify you via text when he is en route</h5>
                </div>
            </li>

            <li class="col-md-4 d-flex flex-column align-items-start p-3 mb-4">
                <div class="cmg-bg-primary rounded p-4 d-flex flex-column">
                    <div class="d-flex justify-content-center align-items-center border rounded-circle bg-light" style="width: 100px; height: 100px; font-size: 24px; font-weight: bold;">
                        5
                    </div>
                    <h5 class="mt-3">Your laundry will be delivered back to you at the allotted time</h5>
                </div>
            </li>

            <li class="col-md-4 d-flex flex-column align-items-start p-3 mb-4">
                <div class="cmg-bg-primary rounded p-4 d-flex flex-column">
                    <div class="d-flex justify-content-center align-items-center border rounded-circle bg-light" style="width: 100px; height: 100px; font-size: 24px; font-weight: bold;">
                        6
                    </div>
                    <h5 class="mt-3">The fastest and most convenient way you’ve ever done laundry</h5>
                </div>
            </li>

        </ul>
    </div>
</section>