Hi,

This can be achieved by using custom javascript. We can enable the button based on the position of the scroll bar. Please try the script below:

document.getElementsByName("licenseAgreement")[0].addEventListener("scroll", checkScrollHeight,false);

function checkScrollHeight(){
    var textElement = document.getElementsByName("licenseAgreement")[0]
    if((textElement.scrollTop + textElement.offsetHeight)>= textElement.scrollHeight){
        document.getElementsByName("button")[0].disabled =false;
    }
}