<script>(function(w,d,t,r,u){var f,n,i;w[u]=w[u]||[],f=function(){var o={ti:"22018554"};o.q=w[u],w[u]=new UET(o),w[u].push("pageLoad")},n=d.createElement(t),n.src=r,n.async=1,n.onload=n.onreadystatechange=function(){var s=this.readyState;s&&s!=="loaded"&&s!=="complete"||(f(),n.onload=n.onreadystatechange=null)},i=d.getElementsByTagName(t)[0],i.parentNode.insertBefore(n,i)})(window,document,"script","//bat.bing.com/bat.js","uetq");</script>

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<script>
        function reportCustomEvent() {
            window.uetq = window.uetq || []; window.uetq.push({ 'ec': 'reservenow', 'ea': 'reservenowclick', 'el': 'reservenowbutton', 'ev': 1 });
        }
    </script>

Add this tag below the UET tag.

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OnClick="reportCustomEvent()"

Add this snippet to the reserve now button.