If it is actually deleted, the only way would be to either restore the project database and repository back to a time when the folder existed OR alternatively you could create a New fresh project in ALM then have the dba restore the old db backup into that new DB schema and then paste the backup of the repository over the repository of the new project. Then essentially you would have a "copy" of the project as it was before and you could use two IE browsers to copy the folder back over from the "new" project to the original project.

Let me know if this makes sense.

Also here is a post about how to do the same with more detail:

https://eyeontesting.com/answers/accidentally-deleted-tests-test-sets-and-data-can/#gsc.tab=0