When you're ready to leave Siwa (though you can return later), talk to Hepzefa again.
There'll be a bit of banter, a bit of exposition, and then you'll find yourself pulled back to the modern world, via yet another Animus user.
The cyclosporine you need is the medkit on the near table.
You can do other things inthe modern day- hunt down some lost papers, riffle through your laptop files, and take a gander at Bayek's actual mummy, but none of these grant any kind of reward yet. So when you're done poking around, reactivate the Animus and travel back once more.
