Mix up some soapy water and pour or spray it onto the tire However, for a lasting fix, you should seek professional repair or replace the affected tire. It'll bubble around the leak and tell you where it is
What Tire Pressure is Too Low - How Low Is Unsafe to Drive
Fix a flat is for emergencies only, and won't work for leaks outside of the tread, like on the sidewall, tire bead, or valve stem
Or just take it to a tire shop.
Here's how you do it, though Many screw this part up Let all the air out of your tire Throw a jack underneath so you aren't pinching the sidewall
Now the can won't be fighting your residual air pressure, and more will go in