How can I separate multiple files from single file caused by zstd -r folder -o output.zst?

I didn't read enough the manual and run the following command

$ zstd -r folder -o output.zst

The following command gave me back a single file called output

$ unzstd output.zst

The output file has all the contents of the files under the folder concatenated. Is there some tools or programs to un-concatenate the single file into multiple original files? This is the only backup file I have and I need the backup. EDIT: what I really should have run (according to [this thread](https://github.com/facebook/zstd/issues/1526)) is

# for tar version 1.31 and above
$ tar --zstd -cf output.tar.zst folder

# for tar version < 1.31
$ tar --use-compress-program zstd -cf output.tar.zst folder