Hi @silverdarling
You should be able to do it like this:
add_action('acf/input/admin_head', 'my_acf_modify_wysiwyg_height');
function my_acf_modify_wysiwyg_height() {
?>
<style type="text/css">
.acf-field-1234567890abc iframe{
height: 600px !important;
}
</style>
<?php
}
Where acf-field-1234567890abc
is the element ID of your WYSIWYG field.
Thanks 🙂