Hello Arthur, you have to contact support.
This is what Support said regarding this issue.
Ben here with the Webflow Customer Support Team!
First, our sincerest apologies for our delay in response. Lately, we have been experiencing higher than normal volume. I know this is no excuse, but we definitely appreciate your patience while we navigate through this time.
I took a look at your site and I think I see the problem. It looks like you experienced a bug with our backup and restore.
After talking with engineers, we may not be able to open up access to your current site. But, I was able to make a copy of the last good back and I can transfer that to you.
In order to transfer, you’ll need to delete a site from your Dashboard so I can transfer this site.
Once you have the backup added to your Dashboard and can confirm the site looks good, I can transfer the hosting and the domain from your current site to this new project.