<h5>Div-1</h5>
<button class="btn btn-primary mb-3" onclick="refreshBid()">Refresh Ad Unit</button>
<div id='div-1'>
  <script type='text/javascript'>
    googletag.cmd.push(function() {
      googletag.display('div-1');
    });
  </script>
</div>
   
  
    var sizes = [
    [300, 250]
];
var PREBID_TIMEOUT = 1000;
var googletag = googletag || {};
googletag.cmd = googletag.cmd || [];
var pbjs = pbjs || {};
pbjs.que = pbjs.que || [];
var adUnits = [{
    code: '/19968336/header-bid-tag-0',
    mediaTypes: {
        banner: {
            sizes: sizes
        }
    },
    bids: [{
        bidder: 'appnexus',
        params: {
            placementId: 13144370
        }
    }]
}];
pbjs.que.push(function() {
    pbjs.addAdUnits(adUnits);
});
var slot1;
googletag.cmd.push(function() {
    slot1 = googletag.defineSlot('/19968336/header-bid-tag-0', [[300, 250]], 'div-1')
        .addService(googletag.pubads());
    googletag.pubads().disableInitialLoad();
    googletag.pubads().enableSingleRequest();
    googletag.enableServices();
});
function refreshBid() {
    pbjs.que.push(function() {
        pbjs.requestBids({
            timeout: PREBID_TIMEOUT,
            adUnitCodes: ['/19968336/header-bid-tag-0'],
            bidsBackHandler: function() {
                pbjs.setTargetingForGPTAsync(['/19968336/header-bid-tag-0']);
                googletag.pubads().refresh([slot1]);
            }
        });
    });
}
   
  
    <html>
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Individual Ad Unit Refresh / Infinite Scroll</title>
    <!-- required scripts -->
    <script async src="//cdn.jsdelivr.net/npm/prebid.js@latest/dist/not-for-prod/prebid.js"></script>
    <script async src="https://securepubads.g.doubleclick.net/tag/js/gpt.js"></script>
  </head>
  <body>
  
  <!-- javascript -->
  <script>var sizes = [
    [300, 250]
];
var PREBID_TIMEOUT = 1000;
var googletag = googletag || {};
googletag.cmd = googletag.cmd || [];
var pbjs = pbjs || {};
pbjs.que = pbjs.que || [];
var adUnits = [{
    code: '/19968336/header-bid-tag-0',
    mediaTypes: {
        banner: {
            sizes: sizes
        }
    },
    bids: [{
        bidder: 'appnexus',
        params: {
            placementId: 13144370
        }
    }]
}];
pbjs.que.push(function() {
    pbjs.addAdUnits(adUnits);
});
var slot1;
googletag.cmd.push(function() {
    slot1 = googletag.defineSlot('/19968336/header-bid-tag-0', [[300, 250]], 'div-1')
        .addService(googletag.pubads());
    googletag.pubads().disableInitialLoad();
    googletag.pubads().enableSingleRequest();
    googletag.enableServices();
});
function refreshBid() {
    pbjs.que.push(function() {
        pbjs.requestBids({
            timeout: PREBID_TIMEOUT,
            adUnitCodes: ['/19968336/header-bid-tag-0'],
            bidsBackHandler: function() {
                pbjs.setTargetingForGPTAsync(['/19968336/header-bid-tag-0']);
                googletag.pubads().refresh([slot1]);
            }
        });
    });
}
</script>
  <!-- html -->
  <h5>Div-1</h5>
<button class="btn btn-primary mb-3" onclick="refreshBid()">Refresh Ad Unit</button>
<div id='div-1'>
  <script type='text/javascript'>
    googletag.cmd.push(function() {
      googletag.display('div-1');
    });
  </script>
</div>
  </body>
</html>