Profile: grampiano

Hi there how do you add fields to the contact us page for nop commerce step by step im new to nop commerce I tried to add a field in ProductContactUs.cshtml but i got a error

Plugins/SevenSpikes.Nop.Plugins.NopQuickTabs/Views/ProductTab/_ProductContactUs.cshtml

the field i added was postaladdress like so

                         <div class="inputs">
                            @Html.LabelFor(model => model.PostalAddress)
                            @Html.TextAreaFor(model => model.PostalAddress, new { @class =
                            "postaladdress", placeholder = T("ContactUs.PostalAddress.Hint") })
                            @Html.RequiredHint()
                            @Html.ValidationMessageFor(model => model.PostalAddress)
                            </div>

Where else should I add the field. Thanks in advance