I've used website builder to make a new site but want to keep the old web address

As per the email I received I've made a new website using website builder but had to use a catchy www.lost.homesteadcloud.com address instead of my usual site name . How do I now give this new site my normal www.lost.com address?  Do I have to delete the lost.com address completely from the old site builder so it is then free for me to claim for the new website builder or will I be left with nothing but tears and potentially lose that domain name forever- I don't mind using the new website builder but I do want to keep the web addrewss I've been using for 10 years!