Hello
To amend try adding the following to the
Head Custom Code field of your templates parameters (Extensions -> Template Manager -> YourTemplate -> Custom Code -> Head Custom Code)...
<script>
document.addEventListener("DOMContentLoaded", function() {
const logo = document.querySelector(".logo-image");
logo.setAttribute('alt', "Your new alt tag");
});
</script>
Replace 'Your new alt tag' with the text of your choice.
Ciaran