Semantic Elements for SEO
Search engines look at the hierarchy of your site (next to the content) to add meaning.
An html site is made up from different tags or elements like div, h1, a, p, etc. These tags are mostly used to add layout and styles to your page, but search engines use them to analyze what's important as well.
For example, search engines know that an h1 is a big title and therefore much more important than a simple paragraph. But it also knows that if there are many h1s on the page you might be trying to game them.
So it's important to pick the right tags for the right things, which Framer does by default for you as well as it can (styles are connected to the right tags). But you can optimize this even further per element by switching up div elements for header or footer tags, so the robots know what's what.
Unfortunately Framer can't do this for you. So you have to simply select the element you want to change the tag for, scroll to the accessibility panel and change the tag:
An additional reason to do this (and the reason that you do this from the accessibility panel) is that adding semantic meaning to your page also helps browsers be more helpful for users who for example are visually impaired, making sure everyone can enjoy your content.