Hello,

In order to change the icon try to configure this selector:

.woodmart-buttons .woodmart-add-btn>a:before {
    content: "\f11d";
    font-family: woodmart-font;
    font-size: 21px;
}

You need to replace font family and icon code. Icon code is taken here https://fontawesome.com/v4.7.0/icons/ enter the icon and find code like this “f11d”

Best Regards