Jak upravit funkci validate pro mé pužití

 if (currentTab >= x.length) {
        // ... the form gets submitted:
        $("#loader").show();
        alert("Jede");
        document.getElementById("inquiryForm").submit();
        return false;
    }

var imageIndex = 0;
/* Custom inquiry js */
var currentTab = 0; // Current tab is set to be the first tab (0)
showTab(currentTab); // Display the current tab

function showTab(n) {
    // This function will display the specified tab of the form...
    var x = document.getElementsByClassName("tab");
    x[n].style.display = "block";
    //... and fix the Previous/Next buttons:
    if (n == 0) {
        document.getElementById("prevBtn").style.display = "none";
    } else {
        document.getElementById("prevBtn").style.display = "inline";
    }
    if (n == (x.length - 1)) {
        //document.getElementById("nextBtn").setAttribute('type', 'submit');
        document.getElementById("nextBtn").innerHTML = "Získat cenu a dárek";
    } else {
        document.getElementById("nextBtn").innerHTML = "Další otázka <i class='icon-circle-arrow-right'></i>";
    }
    //... and run a function that will display the correct step indicator:
    fixStepIndicator(n)
}

function nextPrev(n) {
    // This function will figure out which tab to display
    var x = document.getElementsByClassName("tab");
    // Exit the function if any field in the current tab is invalid:
    if (n == 1 && !validateForm()) return false;
    // Hide the current tab:
    x[currentTab].style.display = "none";
    // Increase or decrease the current tab by 1:
    currentTab = currentTab + n;
	var numberStep = 1 + currentTab;
	var next_class = ' next_inquiry' + numberStep;
    document.getElementById("number").innerHTML = numberStep;
    document.getElementById("next").className =
        document.getElementById("next").className.replace
        ( /(?:^|\s)next_inquiry([0-9]{0,8})/g , next_class );
    // image slider
    //imageIndex = (imageIndex + images.length -1) % (images.length);
    $("#image").attr('src', images[currentTab]);
    if (currentTab >= x.length) {
        // ... the form gets submitted:
        $("#loader").show();
        alert("Jede");
        document.getElementById("inquiryForm").submit();
        return false;
    }
    // Otherwise, display the correct tab:
    showTab(currentTab);
}

function validateForm() {
    // This function deals with validation of the form fields
    var x, y, i, valid = true;

    x = document.getElementsByClassName("tab");
    y = x[currentTab].getElementsByTagName("input");
    // A loop that checks every input field in the current tab:
    for (i = 0; i < y.length; i++) {
        // If a field is empty...
        if (y[i].type !== "file" && y[i].value == "") {
            // add an "invalid" class to the field:
            y[i].className += " invalid";
            // and set the current valid status to false
            valid = false;
        }
    }

    // If the valid status is true, mark the step as finished and valid:
    if (valid) {
        document.getElementsByClassName("step")[currentTab].className += "finish";
    }
    return valid; // return the valid status
}

function fixStepIndicator(n) {
    // This function removes the "active" class of all steps...
    var i, x = document.getElementsByClassName("step");
    for (i = 0; i < x.length; i++) {
        x[i].className = x[i].className.replace("active", "");
    }
    //... and adds the "active" class on the current step:
    x[n].className += " active";
}

 <div id="next" class="col-lg-4 col-md-4 next_inquiry0">
                                                                <button n:name="submit" class="button button-medium button-rounded" type="button" id="nextBtn" onclick="nextPrev(1)">Další otázka </button> <br />
                                                            <p><a href="javascript:void(0);" id="prevBtn" onclick="nextPrev(-1)"><u>Vrátit se k přechozí otázce</u></a></p>
                                                        </div>

 <form n:name="inquiryForm" id="inquiryForm" class="validate-form">

if (n == (x.length - 1)) {
        document.getElementById("nextBtn").setAttribute("type","submit");
        document.getElementById("nextBtn").innerHTML = "Získat cenu a dárek";
    } else {
        document.getElementById("nextBtn").setAttribute("type","button");
        document.getElementById("nextBtn").innerHTML = "Další otázka <i class='icon-circle-arrow-right'></i>";
    }