微信小程序内怎样增加和后台客服联系功能

 <button open-type=&#39;contact&#39; session-from=&#39;&#39;>客服-联系我们</button>

<button class="kf_button" open-type="contact" session-from="weapp">
 <image class="kf_image" src="../../resources/img/kf.PNG"></image>
</button>

.kf_button{
 background-color: rgba(255, 255, 255, 0);
 border: 0px;
 height: 100rpx;
 right: 0;
 bottom: 20rpx;
 position: fixed;
}
.kf_button::after{
 border: 0px;
}
.kf_image{
 z-index: 9999;
 width: 100rpx;
 height: 100rpx;
}