I know that mouth-to-mouth resuscitation wasn't a thing until the 1700's, so I feel as though I'm answering my own question but...maybe someone knows of something people did back then to try to save a drowning victim?
One very odd method was tobacco-smoke enemas. During the late 18th and early 19th centuries, this technique was pioneered as a way of stimulating respiration. Emergency kits containing a small bellows were stationed along the Thames in London to aid drowning victims.