Unfortunately, if you didn't created a backup of your past version of the content, it's not possible to restore it.
In reviewing your previous conversation, I noticed that you mentioned using the Legacy Builder. Unfortunately, there is currently no official guide for migrating from the Legacy Builder to Slice Machine. This can make the process difficult as there may be confusing and breaking changes that we cannot avoid at this time.
As a result, we recommend that users either continue using the Legacy Builder for older websites and select Slice Machine for newer projects or attempt to create an identical copy of the older repository manually, if they wish to use Slice Machine for older projects. We understand that this process can be quite time-consuming and is not an ideal solution, but it’s the best option for avoiding content loss.
We have approached this topic several times in the forum. You can check out some of these discussions in this thread.
From what I understood, the issue in your case is that you had existing models and content in a Legacy repository. Then, you recreated all the Content models in Slice Machine and pushed the changes to your repository. This action caused Slice Machine to override all the existing models in the repository. Since the JSON structure differs in Slice Machine for Slices, the content will always be removed. There might be an exception with fields appearing at the Custom Types' top level. If you keep the same API ID for each top-level field, the content should remain there. But this won’t be the case for Slices.
To avoid this error in the future, I will share your use case with the team so that we can consider publishing a public post that explains the dangers of mixing these two tools together.