in bootstrap you just add the button classes and it will look like a button
<a class="btn btn-default" ...
However, there is no reason you can’t just copy the onclick attribute to the anchor tag (or “href” as you keep calling it).
From your code in the comments:
<div id='demo'></div>
<a onclick="document.getElementById('demo').innerHTML='Hello JavaScript!'; return false; "> Click Me!> <div class="col-md-4 promo-item item-1"> <h3> Unleash </h3> </div> </a>
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solved HTML turn a link into a button