clase central de botones en bootstrap
<div class="d-flex justify-content-center">
<button type="button" class="btn btn-primary">Center Button</button>
</div>
Tokyo
<div class="d-flex justify-content-center">
<button type="button" class="btn btn-primary">Center Button</button>
</div><div class="text-center">
<button type="button" class="btn btn-primary">My button</button>
</div><div class="text-center">
<button type="button">centered button</button>
</div>