Some of the themes that come with bootstrap studio don't have the footer pinned to the bottom of the page.

The instructions in this link are helpful here: https://forum.bootstrapstudio.io/t/footer-always-at-the-bottom-of-the-page/7517

Basically, create custom sitewide CSS (ie. through a .css file under the styles folder of the design), with the following:

body {
    display: flex;
    flex-direction: column;
    height: 100vh;
}
footer {
    margin-top: auto;
}