How do I center the entire footer?

try to use margin: 0 auto; in the style of the footer div.
or rearrange your html structure to enclose the footer div into the general wrapper.

with a link to your site, you may get more help.
screenshots, even if they are properly linked, are no use.

Many thanks for your first help! My site URL: https://hoikistu.fi. And sry about the screenshot, I didn’t know that WP forum doesn’t accept direct links to image files (.png).

#footer is in .column.footer, and .column is floated left; this disturbs the alignment.
to change this, add this style to style.css, for instance before the .footer style:

.column.footer { float:none; }