As you are currently self-hosted, you are only allowed to run 1 Live URL at a time. If you are looking to migrate your community to a new server, you can utilize a test URL to test this on the new server while you're old one is still running your live community on the old server.
If you are changing your community over to a new domain, you would simply ensure your hosting is setup to handle the new domain and make any DNS and software changes (i.e. change your license URL). If you need our assistance in changing your license URL, please let us know.
I'm afraid, there is not really much more we can assist you with that process due to being self-hosted. There is no 30-day trial for self-hosted licenses.