Check code below and move the marker when I press arrow keys on keyboard:
var map = L.map('map').setView([0, 0], 1);
        var OpenTopoMap = L.tileLayer('https://{s}.tile.opentopomap.org/{z}/{x}/{y}.png', {
            maxZoom: 17,
            attribution: 'Map data: © <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors, <a href="http://viewfinderpanoramas.org">SRTM</a> | Map style: © <a href="https://opentopomap.org">OpenTopoMap</a> (<a href="https://creativecommons.org/licenses/by-sa/3.0/">CC-BY-SA</a>)'
        }).addTo(map)