Since the snake is sick: Do not provide a gradient: keep the temps between 80-85F--do not exceed 85F in either air or contact temperature. Review husbandry care sheets online for the species. Make sure you provide a source of dechlorinated water. Leave it alone as much as possible: do not try feeding it.
If you don't plan on keeping it: give the snake to an animal shelter at your first opportunity: the owner clearly did not want it anymore don't bother looking for them. Some crappy people will dump their unwanted pets pretty much anywhere.
If you do plan on keeping it: you will need to spend the $$$ on Vet treatment and proper equipment/setup.