In the 19th c. there was no sure cure. The syphilis spirochete would not even be identified as the cause of the disease until 1905. Perhaps the most common treatment was mercury, often in the form of calomel, or mercury chloride, which was also used to treat gonorrhea- sometimes taken internally, sometimes rubbed on externally. As syphilis was a dreaded disease, doctors were sometimes not afraid to take drastic measures. Thomas Lowry cites the example of one poor Civil War soldier variously dosed over four months with potassium iodide in sarsaparilla, mercuric chloride compounds, silver nitrate, quinine, and iron, given an emetic to make him vomit, given a powerful laxative to purge his intestines , rubbed with chloroform and even blistered ( probably with mustard) . At the end he was in severe pain and could barely walk.

In 1909 Paul Ehrlich would discover an arsenic compound that proved effective , which he named Salvarsan. That became the standard until penicillin. But even before Ehrlich it seems people tried arsenic. It featured in the trial of Minnie Wallace Walkup. Her husband died of arsenic poisoning in 1884, and when she was accused of murder her lawyer mounted a defense that her husband had been treating himself with arsenic for syphilis. This may not have been true, but the fact that it was used in her defense would indicate that it was not unheard of.

So, you could probably grant yourself poetic license to treat your character with all sorts of bizarre remedies, and you'd still be in keeping with the times.

Lowry, T. P. (2012). The Story the Soldiers Wouldn’t Tell: Sex in the Civil War (Reprint ed.). Stackpole Books.

Parascandola, J. (2009). From Mercury to Miracle Drugs: Syphilis Therapy over the Centuries. Pharmacy in History, 51(1), 14-23. http://www.jstor.org/stable/41112412