Make sure that the HTML and Body elements stretch the full page, give the container a height and display a border for the visual effect. This is only for the example.
html, body {
height: 100%;
}
.container {
height: 500px;
}
.h-100 {
border: 1px dotted #cc2222;
}
Then give the row a height of 100%, the main column a top and bottom margin of auto and all should be well.
<div class="container mt-5">
<div class="row h-100">
<div class="col-sm-12 mt-auto mb-auto">
<div class="row">
<div class="col text-center">
I am Left
</div>
<div class="col text-center">
I am Right
</div>
</div>
</div>
</div>