You can't, unless you have the agency version of Studio. In Freelance versions, that option seems to permanently grayed out. You can only open packages you receive and create return packages.
Is there something specific you are trying to accomplish with a package that you can't do by just sending the elements of the package separately?
Thanks for your prompt response and answer.
No specific need. I was just curious about how PMs were creating transkit packages they send to freelancers.