Slider Option Missing From WP Dashboard

This website https://www.sanskritismartkids.com/ has Slider but has missing option from dashboard. Means the slider is there in the website but no option for it’s modification in WP dashboard. This happens after the most recent WP version update. Now, actually I even don’t know which plugin is used for this slider, as my client had assigned me this project from another developer. Now what I explore till now is that I think this slider is not a plugin based. Is it possible? But when I check the theme’s functions.php file and explore this line of code

// UNF-Slider
include_once(UNF_FRAMEWORK_DIRECTORY .'unf/slider/slider-fields.php' );

So I check for the above file “slider-fields.php” and it has nothing to do with my query.
Next, I check the website’s source code and found this HTML Code:

<div class="row clearfix">
<div class="col-md-12 column">
<div id="desktop-slider">
<div id="homeslider">
<!--start desktop slider-->
<div class="sliderloading sliderloading-desktop">
   <img src="https://www.sanskritismartkids.com/wp-content/themes/toddlers/library/img/loading.svg" alt="loading" height="32" width="32" data-no-retina="">
</div>
<div class="sliderloaded sliderloaded-desktop">
   <a href="#" class="left carousel-control hidden-xs swiper-button-prev">Previous</a>
   <a href="#" class="right carousel-control hidden-xs swiper-button-next">Next</a>
   <div class="swiper-container swiper-desktop">
      <div class="swiper-wrapper">
         <!--First Slide-->
         <div class="swiper-slide">
         </div>
         <!--First Slide-->
         <div class="swiper-slide">
            <!-- Slide Image -->
            <img src="https://www.sanskritismartkids.com/wp-content/uploads/2016/04/slider-1108x386.jpg" class="slideimage" alt="">
            <!-- End Slide Image -->
            <!-- Slide Text -->
            <!-- End Slide Text -->
         </div>
         <!--First Slide-->
         <div class="swiper-slide">
            <!-- Slide Image -->
            <img src="https://www.sanskritismartkids.com/wp-content/uploads/2018/01/Website-Banner6-1100x386.png" class="slideimage" alt="">
            <!-- End Slide Image -->
            <!-- Slide Text -->
            <!-- End Slide Text -->
         </div>
         <!--First Slide-->
         <div class="swiper-slide">
            <!-- Slide Image -->
            <img src="https://www.sanskritismartkids.com/wp-content/uploads/2016/04/slide-1108x386.jpg" class="slideimage" alt="">
            <!-- End Slide Image -->
            <!-- Slide Text -->
            <!-- End Slide Text -->
         </div>
      </div>
   </div>
</div>

So, by this piece of source code I explored the file “desktopslider.php”, and this is the file which is used for the slider. In this file I found the shortcode “echo do_shortcode($unf_slider_shortcode);”. By this it means the slider is plugin based. Then where can be the plugin option in WP Dashboard?

One more thing to add, after all this I think that Swiper JS Slider is being used for the slider, so I think of installing Swiper JS Slider plugin. But I see message “This plugin is not compatible with Your Version of PHP”. Also I got “PHP version update required” message in the dashboard. So I consider Updating the PHP version, with full site backup. Of course! So after updating the php version I installed and activated Swiper JS Slider plugin. But what I see that this plugin has different shortcode then the one mention above. So, please can you guide me tickling this issue?
Thanking you in advance!

NOTE: What my client said about this issue is that I add slides using the plugin from dashboard. But he don’t know which is that plugin.

WP Version: 5.4.1
PHP Version: 7.4

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