Click on the down arrow next to the base icon and choose a new icon.

Also, a little known trick is that if you start your base name with an emoji, that emoji will become the icon for your base.

You cannot upload your own photos nor images nor icons, if that’s what you’re looking to do.

Thank you for your quick answer.

However, I don’t want to change the icon but the Cover Image in the Universe.

If you’re talking about the Airtable Universe, this article should help you out:

Problem is solved. Just click on the Cover Image and Explorer will open.