Overwriting dataset files instead of deletion.

[tanishqvyas]

@shreyapr6 @Raksha-Ramesh
In the current implementation, the nan folder is first deleted and then a new folder is made. We should find a way to overwrite existing content.

[Raksha-Ramesh]

It's deleting because we're using shutil rmtree, right?
We have to find an alternative to that

[tanishqvyas]

@Raksha-Ramesh Yes, exactly. We need to find just one function which simply overwrites if possible.