You can use this code to Code Injection > Footer

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.0/jquery.min.js"></script>
<script>
$(document).ready(function(){
    $('<p class="custom-text">Made by <a href="https://google.com/" target="_blank">@tuanphan</a></p>').appendTo('.header-display-desktop');
});
</script>
<style>
p.custom-text {
    white-space: nowrap;
    font-size: 19px;
}
</style>

You will have a result like this