Microsoft owned Remix3D.com will no longer work after Jan 10, 2020. Remix3d is an Microsoft site which allows users to generate and share 3D objects, which users can use it on Paint 3D, and Other third party apps. As people are now not using the site that frequently and inorder to give better Sharing options like Onedrive, Microsoft has decided to announce the sunset.
So, if you are a Remix3d user then visit the site -> Go to My Stuff section and download the back ups of your files for later use.
As the site will be retired on Jan 10, you won't have access to those files post that.
If you have problems on migrating your details, then you can contact the support team through forums available for Microsoft Remix3D site.
"We advise all users who want to keep their uploaded content to take action and download their existing Remix3D.com 3D models to other file storage and sharing platforms as soon as possible, as Remix3D.com will no longer be available after this date" - Microsoft Quoted on its site.
So, if you are a Remix3d user then visit the site -> Go to My Stuff section and download the back ups of your files for later use.
As the site will be retired on Jan 10, you won't have access to those files post that.
If you have problems on migrating your details, then you can contact the support team through forums available for Microsoft Remix3D site.