I hit the wrong button and says, your colony or moon will disappear in 24 hours. What can I do to reverse this?

You can't reverse it apart from possibly appealing your case to the admins using the webmaster@zorgempire.net email. Don't get your hopes up though.

If it asks you to enter your password, it means you have selected abandon. If it doesn't you have changed the name, remember this to avoid future mistakes.