At the moment there is no officially supported way to change the logo. However, this is a frequently requested feature, so we have a Github issue if you'd like to follow along for any future updates.
There are several threads here in the forums going over ways you can make this customization by changing the source code. Notably this thread tends to be updated quite frequently with instructions for new releases: Replace the kibana logo?
In 7.12.1 the SVG logo lives here: kibana/elastic_mark.tsx at v7.12.1 · elastic/kibana · GitHub
I believe altering this SVG and re-building Kibana would be all you need to do, but this isn't something I've tested.