Bootstrap allows us to align elements by using the utility class float. As we want to align the button to the right side of the text box, we have to use the float-right class.
<button class="btn btn-success btn-lg float-right" type="submit">Submit</button>
Note: Although by default, elements like buttons, are left-aligned still we can use float-left class to mention it specifically. We can also use the class float-none to remove any hierarchical floating.
It is important to note that we are using Bootstrap 4 here, in Bootstrap 3 or Bootstrap 2 we can use the helper classes like pull-left, pull-right to align the elements to the left or right accordingly.