Basically the title, you need to use the skills you have now and be a productive member of society.
I don’t mean go back and show the wheel or try invent germ theory etc.
For example I’m a mechanic i think I could go back to the late 1800s and still fix and repair engines and steam engines.
Maybe even take that knowledge further back and work on the first industrial machines in the late 1700s but that’s about it.
Just washing one’s hands before touching the patient would make a massive difference, alcohol is pretty abundant, willow bark tea for the pain (and contact your local herbalist for other remedies), you could infect people with cowpox to vaccinate them against smallpox, you might even be able to grow some penicillin if you manage to make some rudimentary Petri dishes out of broth or beer wort and happen to have the right spores floating around…
Penicillin isn’t just growing some mold, it was selected for out of literally tens of thousands of strains of mold that were sent in from around the globe to find one that wouldn’t kill the patient. You would, at a minimum, need: microscope optics, glassblowing equipment to perform extractions and purifications, a source of solvents (ether will only go so far), assaying equipment (even old school stuff needs indicators), and enough industrial progress to make and machine steel to be able to scale any of it up.
Just finding the correct strain of mold to begin to produce any form of antibiotics would need a pretty insane amount of hardware to make what we would consider a rudimentary lab in modern times, let alone isolating it in a way that’s safe for human consumption.